1. Locard’s Exchange Principle
“When a person comes into contact with an object or another person, a cross-transfer of physical evidence can occur.”

2. Types of Evidence
Direct/testimonial: firsthand observations (eyewitness account, video camera, confessions)
Circumstantial: indirect evidence; implies a fact, but not directly prove it
Physical – bullets, weapons, impressions
Biological – body fluids, plant parts, hair
Trace evidence

3. Trace Evidence
Small but measurable amounts of physical or biological material found at a crime scene

4. Examples of trace evidence
Human hair
Animal hair
Fibers
Soil or plant material (pollen)
fingerprints
Body fluids (semen, blood, saliva, mucus)
Paint chips
Broken glass
Chemical residue

5. Categories of Evidence
Class Evidence
Narrows identity to a group of persons or things
Example: blood type
Individual Evidence
Narrow identity to a single person or thing
Example: fingerprint

6. Crime Scene Investigation

7. The Crime Scene Investigation Team
Who is at the crime scene?
Police and possibly a district attorney.
Crime scene investigators.
Medical examiners.
Detectives.
Specialists.

8. The Seven S’s of Crime Scene Investigation
Secure the scene.
Separate the witnesses.
Scan the scene.
See that photos are taken.
Sketch the scene.
Search for evidence.
Secure the collected evidence.

9. Secure the crime scene

10. Separate the witnesses
Do not allow witnesses to talk to each other
Witness accounts will be compared
Avoid witnesses working together to create a story
Asked: who, what, where?

11. Scan the scene Determine primary and secondary crime scenes
Primary: where murder took place
Secondary: where corpse was found
Where should photos be taken?
Wear protective gear to prevent contamination of crime scene

12. Mark Evidence with Tents

13. See that photos are taken: Crime Scene Photography
Show the scene exactly as it was when you first saw it
If something was moved before you arrived, don’t try to reconstruct the scene – just take the pictures the way you see it
Be careful not to destroy any evidence while taking photos

14. Outside the Scene Exterior of building Arial photos
Pictures of all doors, windows and exits

15. Overall Shots – Outside the Scene

16. Inside the Scene Begin with a view of the entrance
Then photograph the scene as it appears when you first step into the room
Next, move around the room to get photographs of all the walls (also show positions of any possible pieces of evidence)
Photos of other rooms connect with crime scene

17. Overall Shots – Inside the Scene

18. Items of Evidence Take 2 shots:
Midrange shot: show how the item is related to its surroundings
Close-up: bring out details of item
Take 2 close-up shots if marking or measuring device is used
One shot without device, one shot with device

19. Evidence: Knife (possible weapon)
Midrange Photo
Close-Up (with ruler)

20. Sketch crime scene Make accurate rough sketch
Note direction (N) and scale of distance
Include relevant objects (body, doors, windows, furniture, immovable landmarks)
Make final copy (on computer) for court N

21. Search for evidence Grid, strip or lane, spiral search pattern
Use flashlight to find hair and fibers
Use forceps, vacuum cleaner to collect evidence
Grid
Strip or Lane
Spiral

22. Secure the collected evidence
Properly package, seal, and label ALL evidence!
Liquid: airtight, unbreakable containers
Wet items (biological): dry out in breathable container
Dry item: bindle  plastic or paper container
Seal with tape and labeled with pertinent info

23. Packaging Evidence Bindle: folded paper used to hold trace evidence
Crease a clean paper and place the evidence in the X position (as shown above).
Fold in the left and right sides, and then fold in the top and bottom.
Put the bindle into a plastic or paper evidence bag affixing a seal over the opening.
Write your name on the seal.

24. Chain of Custody
In order to present credible evidence in court, a chain of custody log is essential.
A person bags the evidence, marks it for identification, seals it, and signs it across the sealed edge.
It is signed over to a technician in a lab for analysis who opens it, but not on the sealed edge.
After analysis, the technician puts it back in the evidence bag, seals it in another bag, and signs the evidence log (above, right).

26. Crime Scene Evidence Direct or circumstantial evidence?
Physical or biological evidence?
Class or individual evidence?