Forensics Unit 0 : Becoming a Forensic Scientist

Goals of Crime Scene Investigation

1. Determine what happened

2. Recognize probative evidence

3. Document evidence locations

4. Collect and preserve evidence

5. Maintain chain of custody

Testimonial Evidence

Collected from responding officers, eyewitnesses, and/or victims

Physical Evidence

Any physical object/item visible or invisible to the naked eye, such as fingerprints, hair, blood, etc.

Direct Evidence

Evidence that comes from direct proof of a fact

Circumstantial (Indirect)

Evidence that infers the existence of another fact to be true or untrue

Secure the Scene

• Make sure crime scene is isolated, secure, and safe - to preserve evidence

• Cordon off the crime scene with crime scene tape

• Limit number of people entering/exiting scene, from one or few secure points

• Make arrests and/or get medical assistance

Separate the Witness

• Each witness must be kept separate and interviewed individually so their accounts of the events do not influence the other’s

• Prevents witnesses from creating cover stories or sharing details about the crime

Scan the Scene

• Take in the overall scene

• Identify the primary crime scene and any secondary crime scenes

• Look for physical evidence

• Record written notes

• List of everything found

• Condition of the scene

• May make an audio or video recording

• Photographs required

• Measure the perimeter of the scene 

• Each piece of evidence must be measured from two (preferably fixed) points

See the Scene

• Crime Scene photographs must be taken before anything is moved from the scene

• Include evidence markers and rulers/scales in every picture

Overview Photograph

Want the whole scene in view; include points of exit/entry, include walls and adjacent rooms

Victim(s) Photograph

• Position and location relative to the scene from at least two 90 degree locations

• Close-up depicting injuries

• Close-up of weapons or objects near the body

Physical Evidence Photographs

• Wide-angle photo to show position and location relative to the crime scene

• Close-ups to record the details of an object

• A ruler or measuring scale must be present

Sketch the Scene - rough draft

• Needs perimeter and compass directions

• General location of evidence within the scene

Sketch the Scene - final sketch

• Done to scale using measurements from notes

• Objects are assigned letters or numbers, so the sketch isn’t cluttered using a key

• Sketch will be drawn so north points up

Search the Scene

• Employ a search pattern to ensure nothing was overlooked in any of the previous steps

• There is no one way to search for evidence

Secure and Collect All the Evidence

Once all evidence has been documented, it may then be individually packaged, labeled with chain of custody, and sealed