Forensic Science

Learn how science is applied to law enforcement

Forensic Science Information

Key Terms (I)

Glossary

Accessory: A person who knows of a violation of the law and assists the perpetrator in avoiding arrest, trial, or punishment.

Accomplice: An individual who is equally responsible for a violation of the law.

Admissibility: Regarding forensic science, the reliability and truthfulness of the information presented by a forensic scientist.

American Academy of Forensic Sciences: The largest forensic organization in the world.

Anthropometry: A procedure that requires taking bodily measurements to distinguish one individual from another.

Blood Types: A, B, AB, and O are the four blood types. The types differ based on the location of the A and B antigens. These types are also denoted as positive or negative depending on the presence of the Rh factor, a protein.

CSI Effect: The dramatization of forensic science in media that makes the public believe that every crime scene will have forensic evidence. Also, it creates the unrealistic expectation that a case can always be helped by forensic evidence.

Crime Scene Laboratories: Laboratories that apply the principles and techniques of the physical and natural sciences to analyze criminal evidence.

Criminalistics

Criminalistics: Applying standard, scientific processing techniques from the physical and natural sciences to evidence examination.

Digital & Multimedia Science: The study of digital forensic evidence and hacking activities.

Digital Multimedia Science

Engineering Science: The investigation of accidents, product failures, and environmental contaminations.

Engineering Science

Forensic Nursing Science: The application of nursing knowledge to investigate crime-related trauma, liability issues, and death.

Forensic Nursing Science

Forensic Science: The application of science to law enforcement. Forensic science can be applied to both civil and criminal cases.

General Forensic Science: The combined forensic sciences that do not fit into narrower fields.

General Forensic Science

Jurisprudence: A section of forensic science composed of individuals with a law degree who have passed the bar exam. These members work with cases that involve forensic science.

Jurisprudence

Locard's Exchange Principle: When two objects contact one another, a cross-transfer of materials occurs that can connect criminals to victims.

Odontology: The application of dental knowledge to identify human remains or determine dental or oral injuries.

Odontology

Pathology/Biology: Knowledge of the life and medical sciences applied to the examination of organisms that are key to crime scenes.

Pathology/Biology

Physical Anthropology: The application of osteology, the study of bone structures, to the examination of crime scene victims and assailants.

Physical Anthropology

Psychiatry/Behavioral Science: The application of the cognitive sciences to the examination of criminal cases to determine competency or mental illness. The application of the cognitive sciences to civil cases to determine involuntary psychiatric commitment, the right to refuse treatment, competence to make medical decisions, and disability compensation.

Psychiatry/Behavioral Science

Questioned Documents: The application of knowledge pertaining to handwriting, writing instruments, writing mediums, and office machine products to analyze criminal evidence.

Questioned Documents

Serology: The study of blood and bodily fluids.

Toxicology: The study of drugs and chemicals and their effects.

Toxicology

Forensic Sections of the American Academy of Forensic Sciences

Forensic Sections

1. Criminalistics

2. Digital and Multimedia Sciences

3. Engineering Science

4. General

5. Jurisprudence

6. Odontology

7. Pathology/Biology

8. Physical Anthropology

9. Psychiatry/Behavioral Sciences

10. Questioned Documents

11. Toxicology

12. Forensic Nursing Science

Inventions

Important Inventions Used in Forensic Science

Microscopes: Commonly used in forensic science for examining firearms, comparing hairs and fibers, examining bullet markings, and examining victims for cause of death.

Chromatography: A chemical technique in which a homogeneous mixture is split into its components based on their attraction to the stationary phase.

Spectrophotometry: An analytical method that is used to measure a chemical's ability to absorb or transmit light.

Electrophoresis: A method used to separate molecules based on size and charge.

Databases: Used to store physical evidence such as fingerprints, markings on bullets and casings, and DNA. Databases allow law enforcement to compare similar evidence.

DNA Profiling: Allows for the precise or near-precise identification of an individual. Requires traces of blood, semen, hair, or saliva.

Organization of Forensic Laboratories in the United States

Organization

· There is no national system for forensic laboratories in the United States. Forensic laboratories are operated by state, county, and city jurisdictions. Some states create networks to link laboratories.

· Forensic laboratories can operate under the direction of police departments, prosecutors or district attorney offices, medical examiners, corners, universities, or independent agencies.

· An increase in forensic laboratories has occurred because assailants are advised of their rights, the immediate right to counsel has reduced the number of confessions given, there has been an increase in crime over time, all drug seizures must be sent to forensic labs, and DNA profiling is now often required.

· Four laboratories exist outside the jurisdiction of the state and local levels.

FBI Forensic Laboratories: Broad investigations

DEA Forensic Laboratories: Primarily used for drug analysis

Bureau of Alcohol, Tobacco, Firearms, and Explosives Forensic Laboratories: Analyzes alcoholic beverages, documents relating to alcohol and firearm excise tax enforcement, weapons, and explosive devices.

US Postal Inspection Service Laboratories: Investigates crimes related to the postal service

These four laboratories assist local, county, and state jurisdictions that request additional support.

Forensic Units

Basic Units

· Physical Science Unit (Application of Chemistry, Physics, and Geology): Uses chemical tests and analytical instrumentation to examine items such as drugs, glass, paint, explosives, and soil.

· Biology Unit (Application of Biology and Biochemistry): Conducts DNA profiling on fluids, hairs, fibers, and botanical material.

· Firearms Unit: Examines firearms, ammunition, and firearm residues.

· Photography Unit: This unit focuses on recording and presenting physical evidence. The unit uses digital imaging and infrared, ultraviolet, and X-ray photography to make invisible information visible.

· Document Examination Unit: Examines documents by their handwriting, typewriting, the paper used, the ink used, visible depressions, erasures, obliterations, and markings.

Optional Units

· Toxicology Unit: Studies bodily fluids and organs to determine if there is a presence of drugs or poisons.

· Latent Fingerprint Unit: Processes and examines the evidence for chance impressions.

· Polygraph Unit: This unit uses a polygraph to measure physiological responses associated with telling the truth or lying. This unit is more closely associated with criminal investigation rather than forensic science.

· Voiceprint Analysis Unit: Studies audio messages to connect a voice to a suspect. This unit uses a spectrograph to transform audio into a visual voiceprint that displays an individual's unique voice pattern.

· Crime-scene Investigation Unit: A specially trained unit that collects, preserves, and brings evidence to the forensic laboratory.

Roles of Forensic Scientists

· One of the primary roles of a forensic scientist is to examine and collect evidence.

· The three ways that criminal cases are solved are through confessions, eyewitness accounts, and evidence. Because evidence must go through the scientific method, it does not have the inherent bias or error that confessions or eyewitness accounts have.

Scientific Method: A strict process that ensures the systematic collection, organization, and analysis of information. This method prevents any inherent bias or error from affecting the final outcome.

· Beyond analyzing evidence, forensic scientists must prove the admissibility of their findings to judges and act as expert witnesses.

Expert Witness: An individual with knowledge in a relevant field that presents their findings to a court. Knowledge may be obtained from experience, training, education, or a combination of all three. Experts cannot render any view with absolute certainty. At best, the most an expert can offer is an opinion based on scientific certainty.

· Judges are the gatekeepers of scientific, technical, and specialized knowledge presented in a court.

· Judges determine the quality of scientific evidence by whether the technique is testable, by the publications supporting the technique, by the usage and relevance of the technique within the scientific community, and by reviewing the standards controlling the technique.

· Several different standards exist when it comes to determining the admissibility of the findings brought forth to the court. Two common standards are the Fyre Standard and the Federal Rules of Evidence.

Fyre Standard: A technique, procedure, or principle must be generally accepted by a meaningful portion of the scientific community.

Federal Rules of Evidence (Rule 702): Expert testimony counts as admissibility if the testimony is based on sufficient facts and data, the testimony is the product of reliable principles and methods, and the witness has applied the principles and methods reliably to the facts of the case.

· Forensic experts cannot use evidence affidavits or laboratory certificates instead of an in-person testimony. This is due to the Sixth Amendment's Confrontation Clause.

Searching the Crime Scene

Key Terms (II)

Corpus Delicti (Body of Crime): A requirement that the government have enough evidence that shows the essential elements of a crime before someone can be charged with that crime.

Crime Scene: The location where a crime was committed or where there is an indication of a crime.

Dynamic Crime Scene: A crime scene in which changes are still occurring or likely to occur. The priority of an officer or investigator at a dynamic crime scene is to stabilize the situation to prevent injuries, loss of life, and loss of evidence. People should be moved to a safe location while evidence should be left alone.

Primary Scene: The location where the crime was originally perpetrated.

Secondary Scene: A location where activities occurred after the initial crime was perpetrated.

Static Crime Scene: A crime scene in which criminal activities have ceased and there are no longer any immediate threats. The priority at static crime scenes is the preservation of evidence. Investigators and officers should focus on not bringing anything new into a static crime scene.

First Responder at the Crime Scene

· The first officer at the scene is responsible for securing and protecting the crime scene.

· The officer's first priority should be to obtain medical assistance for injured individuals.

· Medical workers must follow an indirect path through the crime scene. This indirect path should avoid evidence so it is not disturbed.

· The officer must record statements from victims before the medical team takes them. The officer should also request the medical team record any statements the victims make on their way to the hospital.

· The officer must identify any other individuals and vehicles at the scene.

· The officer should call for backup as soon as possible.

· The officer must set the boundaries around the scene. Boundaries must center around where the crime took place, should include entrances and exits to the premises, should include the suspect's path, and should include any areas containing evidence.

· Yellow tape indicates a crime not involving a homicide. Red tape indicates a crime involving a homicide.

· Throughout this process, the officer must treat the crime scene as an active site and should not let their guard down.

Preventative Measures

Preventative Measures at the Crime Scene

· The boundaries of the crime scene are set by crime scene tape, ropes, traffic cones, and police barricades. These boundaries help prevent unauthorized individuals from entering the crime scene.

· No unauthorized individuals should be allowed into the crime scene including family members of the victim, the media, and even unauthorized members of the police department.

· A log should be kept of individuals who enter and exit the crime scene.

· Crime scene personnel should do their best not to alter the crime scene by participating in activities such as smoking, eating, drinking, or littering.

· The crime scene should be preserved in its original state for as long as possible. To assist in this, faucets and toilets should not be used. Anything that can affect the crime scene's original temperature should not be touched: windows, doors, heaters, and air conditioners. Nothing should be moved, including bodies, unless it poses an immediate threat.

Crime Scene Survey

· Once the crime scene has been secured, it is the role of the lead investigator to obtain an overview of the situation and create a strategy to record and examine the crime scene.

Walk-through: An initial survey conducted by the lead investigator to obtain an overview of the crime scene and develop a plan. Notes must be taken on possible points of entry, possible points of exit, disturbed areas, and any evidence initially located.

· A priority for the investigator is establishing the perpetrator's path. Once that path is established, investigators should follow indirect paths to the center of the scene to avoid destroying evidence.

· Evidence discovered by investigators must be documented, photographed, and marked with reflective number markers. Fragile evidence, shoe or tire marks, should be secured and tagged.

· Investigators should make note of aspects of the crime scene that suggest the timing of the incident.

Questions

Questions Crime Scene Investigators Should Ask

Investigators should come up with basic questions about the crime scene.

· Is the crime scene inside or outside?

· What is the location of the scene?

· What type of building did the crime take place in?

· What type of neighborhood did the crime take place in?

· Are there any unique odors detected?

· Were any of the doors or windows opened?

· Is anything damaged, out of place, or missing from the scene?

· Does any evidence suggest struggle?

· Are electronics off or on?

· Is food present? What stage of preparation is it in?

· Does the scene appear to involve violence?

· What are the contents of the trashcans and ashtrays?

· What is the state of the bathroom and its contents? Are the towels wet or dry? Is the toilet seat up or down?

· Are there any vehicles around? Are their engines hot or cold?

· Are there any locations where a weapon could be hidden?

Command Center

Crime Scene Command Center

Command Center: A hub outside the crime scene boundaries where tasks are assigned, equipment is stored, and communication occurs.

· Tasks given at the command center include locating evidence, processing evidence, examining evidence, photographing the crime scene and evidence, and sketching the crime scene and evidence.

· Tasks must be carried out in a specific order for the processing of the crime scene to be done properly.

Crime Scene Search

· Crime scene searches are dependent on the location and size of the area as well as the actions of the suspects and victims.

· There should be at least one person supervising and coordinating the search of the crime scene.

Types of Searches

Line / Strip Search Pattern: An investigator starts at the corner of one end of the crime scene boundary and walks straight to the other side. Then, the investigator moves slightly along the border and returns to the side they originally started. This method is repeated until the entire area of the crime scene has been searched. This method is best used in scenes with well-established boundaries.

Spiral Search Pattern: The investigator moves in an inward spiral from the boundary of the crime scene to the center of the crime scene or in an outward spiral from the center of the crime scene to the boundary. This method helps to locate footprints leading away from the crime scene in all directions. However, it is nearly impossible to complete a perfect spiral resulting in evidence being missed.

Grid Search Pattern: An investigator does a line search from east to west and then north to south. This search pattern can be completed by two investigators simultaneously: one investigator works east to west while the other works north to south. This pattern is thorough, but the boundaries must be well-defined.

Quadrant / Zone Search Pattern: The scene is divided into zones or quadrants. The divided areas can be further subdivided to allow for more thorough searches. This method is best suited for large areas.

Wheel / Ray Search Pattern: Several investigators move from the center of the scene outward toward the boundaries or from the boundaries inward toward the center of the scene. This is not a preferred search pattern because large areas go unsearched between the rays.

Unique Search Circumstances

Vehicle Searches: Investigators must avoid making contact with surfaces that may contain fingerprints: the doors or steering wheel. If the vehicle is linked to a hit-and-run investigation, The undercarriage and exterior of the vehicle should be searched for a cross-transfer of materials between the victim and the vehicle. If the vehicle was used for criminal transportation, the focus should be placed on the interior. If the vehicle was burglarized, the search should focus on the point of entry. Tool marks and fingerprints are key to investigating vehicle burglaries.

Night Searches: Night searches are extremely difficult due to the inability to determine the boundaries of the crime scene and the increased difficulty of finding evidence. When possible, the scene should be left undisturbed and guarded until morning. If an investigation must take place at night due to inclement weather or other circumstances, floodlights and other light sources should be used.

Locating Evidence at the Crime Scene

· The purpose of searching a crime scene is to look for physical evidence. The circumstances of the case dictate what is searched for.

Evidence: All the means to support or deny an alleged occurrence. Evidence is submitted for investigation where it is either determined to be valid or invalid.

Physical Evidence: A generic term for items and substances of interest found at crime scenes.

Evidence Types:

· Direct Evidence: Evidence that on its own can sufficiently establish an important fact or claim.

· Circumstantial Evidence: Evidence that does not directly establish a fact or claim but can be used to make a reasonable inference about an event or circumstance.

· Corroborating Evidence: Evidence that fortifies already existing evidence.

· For homicides, the search will be centered around the weapon used and any evidence resulting from the contact between the victim and the assailant. Special attention should be paid to bodies and the areas surrounding them.

· For burglaries, the search focuses on locating tool marks at points of entry and exit.

· Most crimes require a systematic and thorough search for latent fingerprints.

· When an investigator finds evidence of interest, they should place a reflective marker nearby, record its location in their notes, photograph the evidence, and then sketch the evidence.

Closing the Crime Scene

· The search ends when the team or lead investigator determines that all pertinent evidence has been located. Once this is announced, the team carries out a final overview survey of the scene.

· Investigators should take an inventory so nothing is lost or left behind.

· All equipment must be retrieved.

· The team should ensure any remaining threats at the scene are dealt with properly.

· Finally, the scene can be released to the proper authorities.

Documenting the Crime Scene

Documentation Methods

· Investigators have a limited amount of time to record the crime scene in its original state.

· The three primary methods of recording a crime scene are notes, photographs, and sketches.

Forensic Documentation Process: The collection, organization, and investigation of visual information through note-taking, photography, videography, sketching, and computer-generated materials.

Notes

· Notes should be uniform: written in black or blue ink, taken within a bound notebook, and made immediately after noticing a detail.

· Investigators should begin taking notes when they receive the call to report to the crime scene. They should identify the person who contacted them, record the time of the call, record any preliminary information, and record the case number.

· Upon arrival, the investigator should record the date and time of arrival, individuals present, and the identities of any other individuals who are contacted.

· Notes should be taken on the personnel movements in and out of the crime scene.

· Notes should be taken on the tasks given to each member of the investigation team, including the beginning and ending time of each task.

· During the walk-through, notes should be taken discussing the original condition of the crime scene.

· Notes should be taken on evidence and any items or fixtures of interest.

· If any evidence has been disturbed by any individuals, it should be noted.

· The person who collects a piece of evidence should note who found the evidence, where it was located, who packaged it, and the time of packaging.

· Notes should be made on whether any of the evidence underwent any field tests or processing measures.

· If there is a body at the crime scene, the investigator should make notes on the condition of the body, the position of the body, the body's appearance, objects found on the body, wounds found on the body, and the time the body was moved by the medical examiner or corner.

· Audio and visual recordings can be faster than handwriting notes; however, digital recordings must always be transcribed.

Photography

· All jurisdictions accept photographs of a crime scene as a form of visual evidence in criminal investigations.

· Forensic photography documents and preserves the crime scene in its original state. The goal of forensic photography is to show the layout of the crime scene, the position and dimensions of evidence, and the physical relationship of objects to the scene and each other.

· Photographs can be used to document biological evidence in its original condition. This is important because biological evidence is often altered after testing.

· Photographs taken from many different angles can show the lines of sight of victims, witnesses, and suspects.

Admissibility requirements for photographs:

· The photograph must represent the crime scene as found

· Any manipulations to the scene or re-creations of the scene must be documented

· It must have bearing on the case in question

· It must not purposely engage the emotions of the jury

Digital Photography

Digital Photography: Photography that utilizes a digital camera. The camera utilizes electronics to capture light and save an image on a microchip. A digital photograph is generated when the light-sensitive microchip inside the camera captures light from the scene. The camera captures picture elements called pixels. The light on each pixel is recorded as an electrical charge number. Then, the camera reads the charge number as information, the data gained from this information is processed into an image, and the image is saved.

Resolution: The level of detail contained in an image. Resolution is directly proportional to the number of pixels in an image. The greater the resolution, the smoother and more detailed the photo.

Megapixel (One Million Pixels): Used to describe a digital camera in terms of sensor resolution.

· It is recommended that crime scene investigators use a digital single lens reflex (DSLR) camera with a minimum of at least 8 megapixels.

· Photographs can be combined to create a 3D panoramic view of the crime scene.

· Digital photos can be enhanced, examined, and manipulated using computer software.

Computer software allows for:

· Adjusting the brightness

· Adjusting the contrast

· Color balancing

· Cropping the image

· Removing items from the image

· Superimposing images upon the original image

· An original copy of the image should always be kept.

· Standard operating procedures should be established to ensure that images taken at a crime scene are taken with integrity and are of high quality.

· Original and manipulated images must have their metadata available.

Lossy Compression: Condenses files by discarding some image information. An example of this type of compression is the Joint Photographic Experts Group (JPEG). This type of compression is used for images that show the general crime scene.

Lossless Compression: Condenses files without discarding image information. An example of this type of compression is tagged image file format (TIFF) and raw image (RAW). This type of compression is used for crime scene images that require a significant amount of detail.

Lenses

Camera Lens: Bends light to focus an image on the digital microchip. The thicker the lens, the greater the ability to bend light.

Focal Length: The distance between the lens and the image projected on the film or microchip.

· As the thickness of the lens increases, the focal length decreases.

· Lenses with longer focal lengths are used for faraway objects that one wants to capture in detail.

Lens types:

· Normal Lens: 50 to 55 mm focal length. This lens is used for most photographs taken at a crime scene. It is also commonly used to take photographs of pieces of evidence from a standard distance.

· Telephoto Lens: 100 mm or greater focal length. Used to capture high-quality images of subjects that are far away.

· Macro Lens: Focal length less than 50 mm and a 1:1 or 1:2 magnification ratio. Used to capture high-quality images of subjects that are extremely close such as fibers or toolmark impressions.

· Wide Angle Lens: Focal length less than 50 mm, typically 35 mm. Used to capture a wider area.

· Multipurpose "Zoom" Lens: 28 to 80 mm focal length. Allows for one to take normal, wide angle, and telephoto photographs without changing lenses.

Aperture and Shutter Speed

· The amount of light gathered by the camera is regulated by the camera's aperture and shutter speed.

Aperture: The size of the diaphragm opening through which light enters the camera.

F-number: Equal to the focal length of the lens divided by the diameter of the aperture. The f-number is used to adjust the aperture setting. Because the f-number and the aperture are inversely proportional, the lower the f-number, the wider the aperture. The wider the aperture, the more light that is let into the camera.

F-stop: Standard f-number settings. Each f-stop represents a twofold difference in the amount of light entering the camera. The smaller the f-stop number, the larger the aperture.

Shutter: Controls the exposure of the film or microchip to light.

Shutter Speed: The length of time that the microchip is exposed to light. Shutter speed is typically measured in fractions of a second such as 1/2, 1/4, or 1/8.

Depth of Field

Depth of Field: The amount of area in the foreground and background that are in focus with the subject.

· Forensic photographers should strive to maximize depth of field.

· The smaller the aperture, the greater the depth of field. Consequently, the higher the f-stop, the greater the depth of field.

Illumination

Illumination: Light falling on an object in a photograph.

Color Temperature: The measure of the "degree of whiteness" of a light source compared to a perfect white light.

White Balance: Compensates for color temperatures that deviate from white.

· Illumination can be ambient (natural) or artificial.

Additional Photography Tools

Light Meters: Devices used to measure the amount of light in a shot.

Flash: Generates artificial light when ambient light is not good enough.

Filters: Enhance specific elements in a picture or show elements that aren't normally visible in a picture

Filter Types:

· Barrier Filter: Prevents one type of wavelength (color) from reaching the film or microchip. The filter makes areas containing that color lighter. Used when an evidence feature is difficult to see against a surface with a specific color.

· Bypass Filter: Allows only a small range of wavelengths to reach the film or microchip.

· UV Filter / IR Filter: Allows for unseen evidence features to be seen.

· Complementary Color Filter: Makes certain areas of a subject darker.

· Polarizer Filter: Manages glare and reflections

· Polarizing Filter: Eliminates glare

Tripods: Eliminates shaking effect from an unsteady hand. Tripods are required for shutter speeds less than 60 (1/60 seconds).

Scales: Allows for the measurement of objects at a crime scene.

Forensic Photography Considerations

· Evidence should not be reintroduced into the crime scene for photography purposes.

· A photography log should be kept that contains the details of each photograph taken at the crime scene.

· Forensic photographers should strive to fill the frame, avoid shadows, maximize the depth of field, and take photographs in a logical sequence.

Composition: Viewpoint and elements included and excluded in an image.

Order of Photography at the Crime Scene:

· (1st) Overview Photographs: Photos taken of large areas within the scene. These photos inform where the crime took place, where evidence is in relation to certain fixtures, and provide insight into the evidence itself.

· (2nd) Medium Range Photographs: Photos taken of smaller significant areas within the scene.

· (3rd) Close-up Photographs: Show the greatest detail of evidence and objects. Macro lenses and close-up filters are typically used for these photos. Additional close-up photos should be taken using a scale.

Bracketing: Taking a series of pictures of the same subject that vary only in exposure. Bracketing helps to capture the correct exposure at a crime scene.

Videography

Video Documentation: Combines note-taking with photography but cannot replace the details produced by a photograph.

Sketches

· Once the investigator has taken sufficient notes and photographs, the crime scene is sketched.

· The sketch should clearly show the layout of the crime scene and the spatial relationships of all fixtures and objects.

Rough Sketch

Rough Sketch: The initial sketches produced at a crime scene. These sketches must accurately depict the dimensions and locations within the crime scene; however, rough sketches do not have to be aesthetically appealing.

Tools required for sketching:

· Graph or drawing paper

· A measuring tape

· Pencils

· Ruler

· Compass or GPS

Sketch requirements:

· Legend: This section contains the key to the identity and dimensions of objects or evidence. The legend details what evidence or objects correspond to which specific identifiers: numbers, symbols, or letters.

· Compass: Should show an arrow to denote north

· The Body: Contains the drawing itself and all objects within

· The Title Block: A block that contains the case number, agency number, name of the artist, title of the artist, location of the scene, date, and time. This area may also state the victim's name, the names of any suspects, and the type of crime.

Creating the sketch:

· Define the boundaries of the crime scene

· Walls and boundaries should be drawn first

· Walls and boundaries should be measured, typically in inches and feet

· Establish fixed points from which to measure the locations of objects and evidence

Types of Measurement Techniques for Objects

Rectangular Method: Measures two distances from fixed points to an object. This method should generate a right angle. The fixed points are typically walls.

Triangulation Method: Measures the distance of an object from two fixed points. The two fixed points are of a known distance from each other. This method forms a triangle.

Baseline Method: Two fixed objects on opposite sides of the crime scene are located (designated A and B). A line is made between them and measured. Each object has a line drawn to it from the baseline making a 90-degree angle. The distance from the baseline to the object is measured along with its point of intersection with the baseline.

Polar Coordinates Method: Uses only one reference point. The sketch should show the distance and angle at which an object is located in the scene relative to the reference point

Finished Sketch

Finished Sketch: A perfected rough draft that is constructed with aesthetics in mind. The final sketch should also be drawn to scale.

· An indoor sketch should show floors, doors, windows, and any evidence found on the floor.

· An outdoor sketch should be like an ariel view of the scene.

· The final sketch can be drawn by hand or can be computer-made.

Computer-aided Drafting (CAD): The process of creating a scaled crime scene drawing using computer software. Computer-aided drafting has become the standard method for reconstructing crime scenes from rough sketches.

Firearms, Tool Marks, and Impressions

General Overview (I)

General Overview

· Minute markings on surfaces can impart individual characteristics to objects.

Structural variations and irregularities are caused by:

· Scratches

· Nicks

· Breaks

· Wear and tear

Firearm Identification: A forensic discipline concerned with determining if a bullet or cartridge was fired by a particular weapon.

Classifying Firearms

Handguns

Handguns/Pistols: Designed to be held and fired with one hand.

Handgun Types

Single-shot Handguns: Handguns that can only fire one round at a time. Each round must be manually loaded into the chamber before firing.

Revolvers: Handguns that have several firing chambers located within a revolving cylinder. As the revolver is fired, the cylinder rotates. Each firing chamber holds one cartridge. The cartridge is lined up with the barrel when fired. The cartridge cases must be manually ejected to reload the chambers. Swing-out revolvers have a cylinder that swings out to the side. Break-top revolvers are hinged so the barrel and cylinder flip downwards. Solid-frame revolvers use a gate at the back of the gun that allows each chamber to be loaded one at a time.

Semi-automatic Handguns: Semi-automatic handguns fire one shot per trigger pull. Semi-automatic handguns feature a removable magazine. Once the magazine is loaded, the hammer is cocked by pulling the slide on the gun rearward and then releasing it to load the first round. The firing of the cartridge generates gases that are used to eject the cartridge case, cock the hammer, and load the next round.

Automatic Handguns: Handguns that fire as long as the trigger is pressed or until the ammunition is depleted.

Handgun Classifications

Single-action Firearms: Require the hammer to be manually cocked backward each time before the trigger is pulled to fire the weapon.

Double-Action Firearms: Pulling the trigger both cocks and releases the hammer.

Long Guns

Long Guns: Firearms meant to be fired while resting on the shoulder. Long guns include rifles and shotguns which primarily differ by ammunition type and barrel.

Shotguns

Shotguns: Long guns with smooth barrels that have no grooves or lands. Shotguns use a type of ammunition called a shell that contains numerous ball-shaped projectiles called shot. Shotguns can be single-barreled or double-barreled. Double-barreled shotguns can have their barrels arranged horizontally or vertically.

A shotgun barrel can be narrowed toward the muzzle to concentrate the shot when fired. This narrowing is known as the choke.

Long Gun Classificiations

Single-shot Long Guns: Can chamber and fire only one round at a time. The round must be loaded manually each time.

Repeating Long Guns: Uses an instrument to eject spent cartridges, load a new round, and cock the hammer after a round is fired. Repeating long guns include lever-action, pump-action, slide-action, bolt-action, semiautomatic, and automatic long guns.

· Semi-automatic long guns use the force of the gas produced during firing to eject the spent cartridge, load a new round, and cock the hammer. Semi-automatic firearms use a disconnector mechanism to fire one shot per trigger pull.

· Automatic long guns fire multiple consecutive shots with a single trigger pull.

Bore Comparison

· The inner surface of handgun and rifle barrels have markings that are imparted to the bullet after it passes through the barrel.

Gun Barrel: Produced from a solid steel bar that has been hollowed out by drilling.

· Irregular, random marks are imparted onto the barrel from drilling.

Bore: The interior of a firearm barrel.

Rifling: The barrels of handguns and rifles are impressed with unique, spiral grooves. The grooves impart a spin to the projectile that keeps it accurate. The areas between the low-lying grooves produced from rifling are lands.

· Unique, random striations are imparted onto the bore of firearms during the rifling process.

Caliber: The diameter of the gun measured between opposite lands recorded in hundredths of an inch or in millimeters.

Bullet Marking Comparison

· Bullets are impressed with unique rifling grooves when fired.

· There is no practical way to directly compare the markings of the fired bullet with the rifling of the gun. Alternatively, test bullets are fired, recovered, and compared to the original bullet.

· If the test bullet and the bullet found at the crime scene have the same class characteristics, the analyst must move on to matching striation markings.

· Grit and rust can alter the marking on bullets.

· Bullets may be examined without an accompanying suspect weapon. Even without the suspect weapon, the make and caliber of a weapon can be determined from a bullet.

· If the bullet appears not to have lost any metal, its weight can be one factor in determining its caliber.

· The number of lands and grooves, the direction of the twist, and the widths of the lands and grooves can eliminate certain weapons from consideration.

FBI General Rifling Characteristics File: Contains listings of rifling class characteristics.

Comparison Microscope: A microscope used to compare two bullets. Essentially two compound microscopes combined into a single unit that feeds both images into a single binocular unit.

Shotgun Shot Comparison

· Shotguns have smooth barrels that don't impress any characteristic markings that can be compared.

· Shotguns generally fire lead balls or pellets known as shot contained in a shotgun shell. A paper or plastic wad pushes the pellets through the barrel when the shell's powder charge is ignited.

· By measuring the diameter of the shot recovered, the examiner can determine the size of the shot used in the shell.

· The size and shape of the recovered wad may reveal the gauge of the shotgun and the manufacturer of the fired shell.

Gauge: Refers to the diameter of the shotgun's bore. Lower gauge numbers correspond to larger bore diameters. The only exception is the .410 Shotgun which refers directly to its bore diameter. The gauge number is inversely proportional to ammo size: a smaller gauge number fires larger ammo.

Cartridge Comparison

· Pulling the trigger of a firearm releases the weapon's firing pin which strikes the primer causing it to ignite the gunpowder. The expanding gases generated by the burning gunpowder propel the bullet forward while simultaneously pushing the spent cartridge case or shell back against the breech face.

Breech Face: Front part of the breechblock that makes contact with the cartridge.

Cartridge/Round: An ammunition unit that is composed of a projectile, a casing, propellant powder, and primer (ignition device).

· After being spent, the cartridge or shell is impressed with markings from the metal surfaces of the weapon's firing and loading systems.

· The shape of the firing pin can be impressed into the spent cartridge case revealing the distortions of the firing pin.

· For shotgun shells, the firing pin, breech face, extractor, or ejector may be impressed onto the brass portion of the shell.

· Other distinctive markings on spent shotgun shells or cartridges may result from metal-to-metal contact with the magazine, the clip, or the firing chamber walls.

Firearm Clip: A device used to store multiple cartridges together as a unit for insertion into the magazine or cylinder of the firearm.

Firearm Magazine: An ammunition storage and feeding device for repeating firearms.

Extractor: The mechanism in a firearm that withdraws a spent cartridge from the chamber.

Ejector: The mechanism in a firearm that throws the spent cartridge from the firearm.

Automated FIrearms Search Systems

Automated Firearms Search Systems

· Because automatic and semiautomatic weapons are expensive, there is a high likelihood that a single weapon will be used in multiple crimes.

· Computerized imaging technology has made it possible to store bullet and cartridge surface characteristics. If crime laboratories are networked, information on bullets and cartridges can be shared.

National Integrated Ballistics Information Network (NIBIN): A joint database operated by the ATF and FBI that contains images and videos of bullets and spent cartridges. The images and videos within the database allow one to compare their evidence with the database's evidence.

Ballistic Fingerprinting: A concept in which a database is created that captures and stores bullets and cartridges test-fired from firearms before they are sold to the public.

Distance Determination

· Ammunition is propelled toward a target by the expanding gases created by the ignition of smokeless powder or nitrocellulose in a cartridge. Under ideal circumstances, all the powder is consumed in the process and converted into gas, but the powder is never totally burned.

· When a firearm is discharged, unburned and partially burned particles of gunpowder and smoke are propelled out of the barrel, along with the bullet, toward the target.

· The distribution of gunpowder particles and other discharge residues around the bullet hole allows one to assess the distance a firearm was fired.

Firearm Distance Determination: The process of determining the distance between the firearm and target, usually based on the distribution of powder patterns or the spread of the shot.

· Powder residue patterns on the victim should be compared to test patterns made by firing the suspect weapon at varying distances. A white cloth or a fabric comparable to the victim's clothing should be used as a test target.

· Gunpowder residue deposits are dependent on the firearm's barrel length, caliber, ammunition, classification, type, and condition.

Noticeable Distance Determination Characteristics:

· When the weapon is held in contact with or less than 1 inch away from the target, a heavy concentration of residue will surround the entrance hole. In this case, loose fibers surrounding the hole will show scorch marks. Additionally, muzzle gases may produce a star-shaped tear pattern around the hole.

· A halo of vaporous lead deposited around a bullet hole may indicate the bullet was fired eighteen inches or less from the target.

· The presence of scattered specks of unburned and partially burned powder grains without any accompanying soot can be observed at distances up to approximately twenty-five inches.

· A weapon fired more than three feet from a target usually does not deposit any powder residues on the target's surface.

· A hole produced by a weapon fired from three feet or more will only show a dark ring around the perimeter of where it entered. The dark ring is known as bullet wipe.

Shotgun Distribution Comparison

· In the absence of the suspected shotgun, the muzzle-to-target distance can be estimated by measuring the spread of the discharged shot.

· Close-range shotgun discharges enter the target as a concentrated mass. The hole will be somewhat larger than the bore of the barrel. As the distance increases, the pellets progressively separate and spread out.

· A 12 gauge spread generally increases one inch for each yard separating the muzzle and target.

· Other factors that affect the distribution pattern of a shotgun include barrel length, shot size and quantity, gunpowder used, and choke.

Choke: An interior constriction at or near the muzzle end of a shotgun used to control shot dispersion. The greater the choke, the narrower the shotgun pattern and the faster and farther the pellets travel.

Gunpowder Garment Comparison

· When garments and other evidence relevant to a shooting are received by the forensic laboratory, the surfaces are examined under a microscope for gunpowder residue. These particles are identifiable by their characteristic colors, sizes, and shapes.

· IR photography or chemical tests can assist in viewing hard-to-see gunpowder particles. The Greiss test can be used to locate nitrite, a product of the incomplete combustion of smokeless gunpowder, and can be used to examine patterns of gunpowder residues around bullet holes. Lead residues can be detected using a solution of sodium rhodizonate followed by spraying the area with an acid.

Primer and Gunpowder Testing

· Traces of gunpowder and primer are shot toward the shooter upon discharging a firearm.

Dermal Nitrate Test: A chemical test used to detect nitrates. The test is no longer common due to materials such as fertilizers, cosmetics, urine, and tobacco all causing the test to show positive.

· Efforts to identify a shooter are now focused on the detection of primer residues deposited on the hand of a shooter, however, individuals who handle a gun without firing it may have these residues on their hand as well.

· If a person discharges a firearm, there will be a high presence of barium and antimony on and around their hand.

· Applying adhesive tape or swabbing an individual's hands can allow one to test for primer and gunpowder residues. Since residues do not remain on the hand for long, individuals must be tested within hours of the firearm being discharged.

· Sensitive analytical instrumentation or a scanning electron microscope (SEM) can be used to detect both primer and gunpowder particles found on the adhesive tape, swab, or clothing of the suspect.

Serial Number Restoration

· Criminalists may have to restore serial numbers when they have been removed.

· If the serial number has not been intensely removed, an etching agent can be applied to reveal the serial number.

· The area containing the removed serial number must be cleaned of dirt and oil and polished to a mirror-like finish.

Collection and Preservation of Firearm-related Evidence

Firearm Collection

· Safety is the priority when handling a firearm.

· Before unloading a weapon, a record should be made of the weapon's hammer and safety position as well as the location of all fired and unfired ammunition.

· For revolvers, the chamber position should be recorded.

· Firearm magazines should be removed from the firearm, checked for fingerprints, and emptied.

· Firearms should have an identification tag attached to the trigger guard indicating the weapon's serial number, the make and model, and the investigator's initials.

· When a firearm is recovered from an underwater location, the firearm should be transported to the laboratory in a receptacle containing enough of the same water to keep it submerged. This process prevents rust from developing.

Cartridge and Bullet Collection

· Bullets, cartridges, and shells should be placed in individual containers or envelopes. The bullet, cartridge, or shell should be wrapped in tissue paper prior to being placed into a container.

· Any trace evidence adhering to bullets, cartridges, or shells should not be removed.

· For incidents involving shotguns, any wads recovered should be packaged and sent to the laboratory.

Clothing Collection

· The clothing of a firearm victim or suspect should be carefully preserved to prevent the disruption of residues.

· Cutting or tearing of clothing in the area of the bullet hole should be avoided.

· Wet clothing should be air-dried out of direct sunlight, folded, and deposited into a paper bag.

Tool Marks

Tool Mark: Any impression, cut, gouge, or abrasion caused by a tool coming into contact with another object.

· Examination of tool marks can reveal important class characteristics including the size and shape of the tool.

· Tools have unique imperfections, such as nicks and breaks, that may appear on the tool mark.

· If the edge of a tool is scarped, it may cut a series of lines that reveals the type of tool used.

· Tool marks are difficult to recreate and require applying the suspect tool to a surface at various angles and pressures to deduce if the tool generates similar markings to the original.

Collecting Tool Mark Evidence

· Whenever practical, the entire object or the part of the object bearing the tool mark should be submitted to the forensics laboratory.

· When it's impractical to remove a tool mark, the mark should be photographed to scale and a cast should be made of the mark. Liquid silicone is the best casting material for reproducing the mark in the most detail.

· Tool marks must be packaged in separate containers.

· Trace evidence should be preserved on the tool and tool mark.

Other Impressions

· Other impressions include shoe, tire, or fabric impressions.

· Before an impression is moved or lifted, it must be photographed at various angles in relation to the overall crime scene.

· When an impression is on a surface that cannot be removed, the impression can be lifted using a lifting material and fingerprint roller or a portable electrostatic lifting device and Mylar film.

· Impressions can only be compared when the suspect item is recovered. The key to comparing the impression and the suspect item is to compare individual characteristics from wear and tear, cuts, gouges, and other damage.

Biometrics

Forensic Biometrics

Biometrics: A system that can accurately and efficiently identify a person using their biological and behavioral traits.

Physiological Biometrics: Focuses on identifying a person based on their unique physical traits by analyzing their fingerprints, hand, iris, retina, or face.

Behavioral Biometrics: Focuses on identifying a person based on their unique behavioral or mental patterns by analyzing their handwriting, voice, keystrokes, and gait.

Fingerprints

· A fingerprint is an individual characteristic. No two fingers have been found that possess identical ridge characteristics.

Minutiae: Ridge characteristics that are studied when characterizing a fingerprint.

· The identity, number, and location of ridge characteristics impart individuality to a fingerprint.

· Most prints recovered at a crime scene are partial impressions that only show a portion of a fingerprint.

Forensic Science

Contents

Forensic Science Information

Documenting the Crime Scene

Searching the Crime Scene

Firearms, Tool Marks, and Impressions

Forensic Science Information

Key Terms (I)

Accessory: A person who knows of a violation of the law and assists the perpetrator in avoiding arrest, trial, or punishment.

Accomplice: An individual who is equally responsible for a violation of the law.

Admissibility: Regarding forensic science, the reliability and truthfulness of the information presented by a forensic scientist.

American Academy of Forensic Sciences: The largest forensic organization in the world.

Anthropometry: A procedure that requires taking bodily measurements to distinguish one individual from another.

Blood Types: A, B, AB, and O are the four blood types. The types differ based on the location of the A and B antigens. These types are also denoted as positive or negative depending on the presence of the Rh factor, a protein.

CSI Effect: The dramatization of forensic science in media that makes the public believe that every crime scene will have forensic evidence. Also, it creates the unrealistic expectation that a case can always be helped by forensic evidence.

Crime Scene Laboratories: Laboratories that apply the principles and techniques of the physical and natural sciences to analyze criminal evidence.

Criminalistics: Applying standard, scientific processing techniques from the physical and natural sciences to evidence examination.

Digital & Multimedia Science: The study of digital forensic evidence and hacking activities.

Engineering Science: The investigation of accidents, product failures, and environmental contaminations.

Forensic Nursing Science: The application of nursing knowledge to investigate crime-related trauma, liability issues, and death.

Forensic Science: The application of science to law enforcement. Forensic science can be applied to both civil and criminal cases.

General Forensic Science: The combined forensic sciences that do not fit into narrower fields.

Jurisprudence: A section of forensic science composed of individuals with a law degree who have passed the bar exam. These members work with cases that involve forensic science.

Locard's Exchange Principle: When two objects contact one another, a cross-transfer of materials occurs that can connect criminals to victims.

Odontology: The application of dental knowledge to identify human remains or determine dental or oral injuries.

Pathology/Biology: Knowledge of the life and medical sciences applied to the examination of organisms that are key to crime scenes.

Physical Anthropology: The application of osteology, the study of bone structures, to the examination of crime scene victims and assailants.

Questioned Documents: The application of knowledge pertaining to handwriting, writing instruments, writing mediums, and office machine products to analyze criminal evidence.

Serology: The study of blood and bodily fluids.

Toxicology: The study of drugs and chemicals and their effects.

Forensic Sections of the American Academy of Forensic Sciences

Important Inventions Used in Forensic Science

Microscopes: Commonly used in forensic science for examining firearms, comparing hairs and fibers, examining bullet markings, and examining victims for cause of death.

Chromatography: A chemical technique in which a homogeneous mixture is split into its components based on their attraction to the stationary phase.

Spectrophotometry: An analytical method that is used to measure a chemical's ability to absorb or transmit light.

Electrophoresis: A method used to separate molecules based on size and charge.

Databases: Used to store physical evidence such as fingerprints, markings on bullets and casings, and DNA. Databases allow law enforcement to compare similar evidence.

DNA Profiling: Allows for the precise or near-precise identification of an individual. Requires traces of blood, semen, hair, or saliva.

Organization of Forensic Laboratories in the United States

· There is no national system for forensic laboratories in the United States. Forensic laboratories are operated by state, county, and city jurisdictions. Some states create networks to link laboratories.

· Forensic laboratories can operate under the direction of police departments, prosecutors or district attorney offices, medical examiners, corners, universities, or independent agencies.

· Four laboratories exist outside the jurisdiction of the state and local levels.

FBI Forensic Laboratories: Broad investigations

DEA Forensic Laboratories: Primarily used for drug analysis

Bureau of Alcohol, Tobacco, Firearms, and Explosives Forensic Laboratories: Analyzes alcoholic beverages, documents relating to alcohol and firearm excise tax enforcement, weapons, and explosive devices.

US Postal Inspection Service Laboratories: Investigates crimes related to the postal service

These four laboratories assist local, county, and state jurisdictions that request additional support.

Forensic Units

Basic Units

· Physical Science Unit (Application of Chemistry, Physics, and Geology): Uses chemical tests and analytical instrumentation to examine items such as drugs, glass, paint, explosives, and soil.

· Biology Unit (Application of Biology and Biochemistry): Conducts DNA profiling on fluids, hairs, fibers, and botanical material.

· Firearms Unit: Examines firearms, ammunition, and firearm residues.

· Photography Unit: This unit focuses on recording and presenting physical evidence. The unit uses digital imaging and infrared, ultraviolet, and X-ray photography to make invisible information visible.

· Document Examination Unit: Examines documents by their handwriting, typewriting, the paper used, the ink used, visible depressions, erasures, obliterations, and markings.

Optional Units

· Toxicology Unit: Studies bodily fluids and organs to determine if there is a presence of drugs or poisons.

· Latent Fingerprint Unit: Processes and examines the evidence for chance impressions.

· Polygraph Unit: This unit uses a polygraph to measure physiological responses associated with telling the truth or lying. This unit is more closely associated with criminal investigation rather than forensic science.

· Voiceprint Analysis Unit: Studies audio messages to connect a voice to a suspect. This unit uses a spectrograph to transform audio into a visual voiceprint that displays an individual's unique voice pattern.

· Crime-scene Investigation Unit: A specially trained unit that collects, preserves, and brings evidence to the forensic laboratory.

Roles of Forensic Scientists

· One of the primary roles of a forensic scientist is to examine and collect evidence.

· The three ways that criminal cases are solved are through confessions, eyewitness accounts, and evidence. Because evidence must go through the scientific method, it does not have the inherent bias or error that confessions or eyewitness accounts have.

Scientific Method: A strict process that ensures the systematic collection, organization, and analysis of information. This method prevents any inherent bias or error from affecting the final outcome.

· Beyond analyzing evidence, forensic scientists must prove the admissibility of their findings to judges and act as expert witnesses.

· Judges are the gatekeepers of scientific, technical, and specialized knowledge presented in a court.

· Judges determine the quality of scientific evidence by whether the technique is testable, by the publications supporting the technique, by the usage and relevance of the technique within the scientific community, and by reviewing the standards controlling the technique.

· Several different standards exist when it comes to determining the admissibility of the findings brought forth to the court. Two common standards are the Fyre Standard and the Federal Rules of Evidence.

Fyre Standard: A technique, procedure, or principle must be generally accepted by a meaningful portion of the scientific community.

Federal Rules of Evidence (Rule 702): Expert testimony counts as admissibility if the testimony is based on sufficient facts and data, the testimony is the product of reliable principles and methods, and the witness has applied the principles and methods reliably to the facts of the case.

· Forensic experts cannot use evidence affidavits or laboratory certificates instead of an in-person testimony. This is due to the Sixth Amendment's Confrontation Clause.

Searching the Crime Scene

Key Terms (II)

Corpus Delicti (Body of Crime): A requirement that the government have enough evidence that shows the essential elements of a crime before someone can be charged with that crime.

Crime Scene: The location where a crime was committed or where there is an indication of a crime.

Primary Scene: The location where the crime was originally perpetrated.

Secondary Scene: A location where activities occurred after the initial crime was perpetrated.

Static Crime Scene: A crime scene in which criminal activities have ceased and there are no longer any immediate threats. The priority at static crime scenes is the preservation of evidence. Investigators and officers should focus on not bringing anything new into a static crime scene.

First Responder at the Crime Scene

· The first officer at the scene is responsible for securing and protecting the crime scene.