Chain of custody
The documented and unbroken transfer of evidence. This process ensures tracking of the evidence as it passes from the crime scene to a courtroom.
Circumstantial evidence
(Indirect evidence) evidence used to imply a fact but not support it directly (EX: can be either physical or biological in nature. Physical evidence includes impressions such as fingerprints, footprints, shoe prints, the impressions, and tool marks. Physical evidence also includes glass, soil, fibers, weapons, bullets, and shell casings. Biological evidence includes blood, DNA in tissue, bodily fluids, hair, plants, pollen, and natural fibers.
Class evidence
Material that connects an individual or thing to a certain group (EX: knowing ABO blood type of a sample of blood from a crime scene tells us that one of many persons with that blood type of a sample of blood from a crime scene tells us that one of many persons with that blood type may have been there.)
Crime-scene investigation
A multidisciplinary approach in which scientific and legal professionals work together to solve a crime
Crime-scene reconstruction
A hypothesis of the sequence of events from before the crime was committed through its commission
Datum Point
A permanent, fixed point of reference used in mapping a crime scene
Direct evidence
Evidence that (if authentic) supports an alleged fact of a case (EX: includes firsthand observations such as eyewitness accounts, dashboard video cameras.)
First responder
The first safety official to arrive at a crime scene.
Individual evidence
A kind of evidence that identifies a particular (individual) person or thing (EX: individual evidence typically has such a unique combination of characteristics that it could only belong to one person or thing, such as a finger print or DNA)
Paper bindle
A folded paper used to hold trace evidence
Primary crime scene
The location where the crime took place
Secondary crime scene
A location other than the primary crime scene, but that is related to the crime; where evidence is found
Trace evidence
Small but measurable amounts of physical or biological material found at a crime scene
Triangulation
A mathematical method of estimating positions of objects at a location such as a crime scene, given locations of stationary objects
The goal of a crime scene investigation
Is to recognize, document, photograph, and collect evidence a the scene of a crime. Solving the crime depends on piecing together the evidence to form a picture of what happened at the crime scene.
Locard's Principle of Exchange
1. Whenever to people come into contact with each other or with an object a physical transfer occurs. Hair, skin cells, clothing, fibers, pollen, glass fragments, debris from a persons clothing, makeup, or any number of different types of material can be transferred from one person or object to another.
2. The second part of Locard's Principle states that the intensity, duration, and nature of the of the entities in contact determine the extent of the transfer. EX: more transfer would occur if two individuals engaged in a fistfight than if a person simply brushed past another person.
Crime Scene investigation team
The team is made up of legal and scientific professionals who work together to solve a crime.
- Police officers: are usually the first to arrive at a crime scene. They secure the scene and direct activity. A district attorney may e called to the scene to determine whether a search warrant is necessary for the crime-scene investigators.
- Crime-scene investigators: document the crime scene in detail and collect physical evidence. Crime-scene investigators record the data, sketch the scene, and take photos of the crime scene.
- Medical examiners (coroners): determine the manner of death: natural, accidental, homicide, suicide, or undetermined.
- Detectives: interview witnesses, and talk to the crime-scene investigators about the evidence.
- Specialists: such as entomologists (insect biologists), forensic scientists, and forensic psychologists may be consulted if the evidence requires their expertise.
1. Securing the scene
The responsibility of the first responding law enforcement officer (first responder). The safety of all individuals in the area is the first priority. Preservation of evidence is the second priority. This means the officer protects the area within which the crime has occurred, restricting all unauthorized persons from entering. Transfer, loss, or contamination of evidence can occur if the area is left unsecured. The officer on scene keeps a security log of all those who visit the crime scene. The officer collects pertinent information and requests any additional requirements for the investigation. And may request more officers or an additional team of experts.
2. Separating witnesses
Witnesses s must not be allowed to talk to each other. Crime-scene investigators will compare the witnesses accounts of the events. Witnesses are separated so they do not work together to create a story.
Questions that are asked of each witness:
- When did the comer occur?
- Who notified law enforcement?
- Who is the victim?
- Can the perpetrator be identified?
- What did you see happen?
- Where were you when you observed the crime scene?
3. Scanning the Scene
The forensic crime-scene examiners first need to scan the scene to determine where photos should be taken. A determination may be made of a primary crime scene and secondary crime scene and priorities assigned regarding examination. A robbery in front of a store might be the primary scene, and the home of a suspect might be the secondary scene. A murder may have taken place at one location (primary scene) and the body found at another (secondary scene).
4. Seeing the scene
The crime-scene examiner needs to see the scene. Photos of the overall area and close-up photos with and without a measuring ruler should be taken. Triangulation should be included in the photos. Triangulation is a mathematical method of calculating the location of an object from the location of other objects. Close-ups and photos from varying distances of any evidence and remains should be taken.
5. Sketching the scene
A crime-scene investigator eventually makes an accurate sketch of the crime scene, noting the position of the remains (if any) and any other evidence. All objects should be measured from two immovable landmarks. On the sketch, north should be labeled and a distance scale should be provided. Any other objects in the vicinity of the crime scene, such as doors, windows, and furniture, should be included in the sketch. if the crime scene is outdoors, the positions of the trees, vehicles, hedges, and other structures or objects should be included in the sketch. Later, a more accurate, final copy of the crime scene should be made for possible presentation in court, likely w/ specialized software.
6. Searching for Evidence
The type of search pattern varies depending on the size of the area to be searched and the number of investigators. Single investigators might use a gridded, linear, or spiral pattern. A group of investigators might use a linear, zone, or quadrant pattern. These patterns are used systematically, ensuring that no area is left unsearched.
Grid search pattern
Is simply two parallel searches, offset by 90 degrees, performed one after the other. Grid searches are used for scenes with well-established boundaries. 1-2 CSI
Linear search pattern
All members of the CSI team form a line. They walk in a straight line, at the same speed, from one end of the crime scene to the other
Quadrant or Zone search pattern
The CSI in charge divides the crimes scene into sectors, and each team member takes one sector. Team members may then switch sectors and search again to ensure complete coverage. Up to 4 CSI
Spiral search pattern
The CSI starts at the perimeter of the scene and works towards the center. Spiral patterns are a good method to use when there is only one CSI at the scene. This is a good method for scenes with defined boundaries or exteriors
7. Securing and collecting Evidence
All evidence needs to be properly packaged, sealed, and labeled. Specific procedures and techniques for evidence collection and storage must be followed. Liquids and arson remains are stored in airtight, unbreakable containers. Moist biological evidence is stored in breathable containers so the evidence can dry out, reducing the chance of mold contamination. After the evidence is allowed to air dry, it is packaged in a paper bindle. The bindle can then be placed in a plastic or paper container. This outer container is then sealed with tape. An evidence log and the signature of the collector written across the tape. An evidence log and a chain of custody document must be attached to the evidence container.
The evidence log should contain pertinent information including:
- Case number
- Item inventory number
- Description of evidence
- Name of suspect
- Name of victim
- Date and time of recovery
- Signature or person recovering the evidence
- signature of any witnesses present during collection
Packaging evidence
The paper bindle is ideal packaging for small, dry, trace evidence. The size of the bindle can be constructed from a sheet of paper. If the evidence is large, the bindle can be constructed from a sheet of wrapping paper. Evidence must be properly handled, collected, and labeled so that the chain of custody is maintained.
Analyze Evidence
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Crime scene reconstruction
Involves forming a HYPOTHESIS of the sequence of events from before the crime was committed through its comission. The evidences examined and compared with the witnesses statements to help determine the reliability of their accounts/the investigator looks at the evidence and attempts to determine how it fits into the overall crime scenario. The evidence does not lie, but it could have been staged. It is important that investigators maintain an open mind as they examine all possibilities.
Staged crime scenes
Crimes scenes that are staged by criminals pose a unique problem. The evidence will not match the testimony of witnesses.
- Arson: perpetrator stages a fire to cover some other crime
- Murder: staged to look like suicide
- Burglary: staged to collect insurance money
Determination of whether a crime is staged the following should be considered
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Conducting a systematic search
The following are often searched for physical evidence:
- Areas of forced entry
- Escape routes/exits
- Suspect
- Victim
- Weapons
- Possible weapon locations
- Vehicles
- Suspects residence
- Primary scene where the assault occurred
- Place where body was removed from
- Secondary scene or body dump locations