Crime Scene Investigation Study Guide

CRIME SCENE

Any physical location in which a crime has occurred or is suspected of having occurred.

Testimonial evidence

Includes oral or written statements given to police as well as court testimony by people who witnessed an event.

Physical evidence

Refers to any material items that would be present at the crime scene, on the victims, or found in a suspect's possession.

Trace evidence

Refers to physical evidence that is found in small but measurable amounts, such as strands of hair, fibers, or skin cells.

Purpose of evidence collected

May prove that a crime has been committed, establish key elements of a crime, link a suspect with a crime scene or a victim, establish the identity of a victim or suspect, corroborate verbal witness testimony, exonerate the innocent, and give detectives leads to work with in the case.

POLICE OFFICERS

Typically the first to arrive at a crime scene, responsible for securing the scene to prevent evidence from being destroyed and detaining persons of interest in the crime.

CSI UNIT

Documents the crime scene in detail and collects any physical evidence.

DISTRICT ATTORNEY or PROSECUTOR

Often present to help determine if any search warrant is required to proceed, and obtain those warrants from a judge.

MEDICAL EXAMINER

May or may not be present to determine a preliminary cause of death in a homicide.

SPECIALISTS

Forensic entomologists, anthropologists, or psychologists who may be called in if the evidence requires expert analysis.

DETECTIVES

Interview witnesses and consult with the CSI unit, investigating the crime by following leads provided by witnesses and physical evidence.

Crime Scene Protocol - Step 1: Interview

The first step is to interview the first officer at the scene or the victim to determine what allegedly occurred, the nature of the crime, and how it was committed.

Crime Scene Protocol - Step 2: Examine

The second step is to identify potential evidence, determine the point of entry and exit, and outline the general layout of the crime scene.

Crime Scene Protocol - Step 3: Document

Involves creating a pictorial record of the scene, as well as a rough sketch to demonstrate the layout of the crime scene and to identify the exact position of the deceased victim or other evidence.

Crime Scene Protocol - Step 4: Process

The last step where the crime scene technician will process the crime scene for evidence, both physical and testimonial evidence.

Locard's Exchange Principle

States that with contact between two items, there will always be an exchange, which is the basis of trace evidence collection at a crime scene.

Individual evidence

Can often prove a direct and strong link between a suspect and a crime scene or victim, such as fingerprints, DNA (except for identical twins), unique tool marks, handwriting, and a torn piece of paper that perfectly matches another piece.

Probative

Means supplying proof or evidence.