The Crime Scene

Principle of Exchange

Dr. Edmond Locard, director of the world’s first forensic lab (1910, Lyon, France), established the idea of the exchange principle; namely that:

1. When a person comes in contact with an object or another person, a cross-transfer of physical material can occur.

2. Study of the material can determine the nature and duration of the transfer.

Types of Evidence

Statements of a witness in court would be direct evidence.

Indirect or circumstantial evidence, such as a fingerprint (physical evidence) or blood or hairs (biological evidence), would imply something, and is called trace evidence.

Trace Evidence

Type of Circumstantial evidence Physical transfer of material Examples:

– Hair– Fingerprints– Soil– Blood– Kleenex– Fiber– Glass– Paint chips

Class Evidence

Narrows an identity to a group of persons or things

Cannot specify a single person Only excludes people that do not fit the category Examples:

– Blood types– Hair color– Common fibers– Shoe prints

Individual Evidence

Narrows identity to a single person or thing Examples:

– DNA– Complete fingerprints (not partials)– Tool marks– Anything torn or broken

and left at the scene

The Five S’s of Crime Scene Investigation

1. Secure the scene. 2. Separate the witnesses. 3. Scan the scene. 4. Sketch and photograph the scene. 5. Search for and collect evidence.

Securing the Scene

The most important job at a crime scenePerformed by the first officer at the scene,

called the first responderSafety of all individuals is first priorityPreservation of evidence is secondFinally record the scene

Separate the witnesses

Separation prevents them talking to each other

Each witness will be asked about the crime scene and what they observed

Scan the Scene

Determine if and where photos should be taken

Determine if there may be a secondary crime scene– Person killed at a party (primary scene)– Dumped in a lake (secondary scene)

Sketching the Scene

First is a Rough Sketch done at the scene Must be accurate and to scale Note body, evidence, doorways, windows,

walls, trees, cars, and movable objects Distances should be measured and recorded Case number, date, location, and time should

also appear on the sketch

Photographing the Crime Scene

Photograph:– All evidence– Doors and windows– Anything out of the

ordinary

Searching and Collecting Evidence

Must be properly packaged, sealed, and labeled

Dry evidence - placed in a paper bindle, put into a plastic bag, sealed with tape, labeled

Wet evidence - placed in a paper bag to allow drying, then treated like dry evidence

When bag is sealed, person must sign their name across the seal

Chain of Custody

Must be attached to evidence container

Starts with person who finds evidence

The next person to use or analyze the evidence must fill out a label

Ensures evidence is handled correctly

If it is not handled correctly, can be traced to who’s responsible

Packaging the evidence

1. Crease a clean paper and place the evidence in the X position (as shown above).

2. Fold in the left and right sides, and then fold in the top and bottom.

3. Put the bindle into a plastic or paper evidence bag affixing a seal over the opening.

4. Write your name on the seal.