Crime Scene PPT.pdf, Summaries of Criminology

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Dr. Edmond Locard : Every criminal can be connected to a crime by small particles carried from the scene.

• Whenever 2 objects come in contact with one another, a cross-transfer of physical evidence can occur.
• The intensity , duration , and nature of the materials in contact determine the extent of the transfer.

Types of circumstantial evidence:

b) Biological evidence: body or body parts, body fluids, hair, leaves or other plant parts, natural fibers, feathers, wood

c) Trace evidence: Small but measurable amounts of physical or biological material found at a crime scene. Examples: strand of hair, fingerprint, DNA, drop of blood, pollen, gunshot residue

a) Physical evidence: synthetic fibers, weapons, bullets, shell casings, paint chips, documents, imprints and prints (shoes, tires, etc.), tool marks, soil, drugs, etc.

Evidence can also be divided into:

Class evidence : narrows evidence to a group of persons or things i.Example: Blood Type- can be A, B, AB, O. Finding one type at a crime scene narrows down the suspects to a smaller group.

Individual evidence : narrows evidence down to a single person or thing. i.Example: Fingerprints, handwriting, DNA, and sometimes physical matches.

Importance of Evidence

i. Can prove a crime has been committed and set the scene for the investigation.

ii. Can back up witness testimony or prove it false. iii. Can link a suspect with a victim or with a crime scene. ii. Can determine the identity of people associated with a crime. ii. Allows investigators to reconstruct a crime.

The Crime Scene Investigation Team:

• First Police Officer on the scene
• Backup Police and possibly a district attorney
• Medics
• Investigator/ Detective
• Medical Examiner
• Photographer and/or Field Evidence Technician
• Lab Experts

Securing the Scene:

The first responding police officer must make sure the scene is secure by first making sure all individuals in the area are safe and second by preserving evidence.

1. Obtain medical assistance if needed 2. Arrest suspects 3. Isolate the area
2. Request additional needs for investigations

Separating the Witnesses:

Witnesses must not be allowed to talk to one another. This prevents them from working together to create a story ( collusion ).

Scan the Scene:

i. Forensic examiners scan the scene to see where photos should be taken. The primary and secondary crime scenes must be determined.

1. The primary crime scene is where a crime actually occurred.
2. A secondary crime scene is in some way related to the crime but is not where the actual crime took place.

See the Scene:

i. A crime scene examiner looks at the scene. The Photography Unit takes photos of the overall area and close up photos with and without a measuring ruler.

Search for Evidence:

Spiral: Grid:

Linear: Quadrant or Zone:

Securing and Collecting the Evidence:

i. All evidence must be properly packaged, sealed and labeled using specific techniques and procedures. ii. Packaging Evidence

1. Metal or plastic forceps may have to be used to pick up small items.
2. Plastic pill bottles with lids are preferred containers for hairs, glass, fibers, and other kinds of trace evidence.
3. Liquids and arson remains are stored in airtight , unbreakable containers.

Evidence Log & Chain of Custody

• Each person who comes in contact with a piece of evidence must use proper procedure and protocol in order to maintain responsible handling of evidence from crime scene to courtroom in order for the evidence to be admissible in court.

Control Samples:

Control samples should also be taken from the victim for purposes of exclusion (blood, hair, etc.)

Standard/Reference Sample- Physical evidence whose origin is known , such as blood or hair from a suspect, that can be compared to crime- scene evidence.