1. Chapter 2 Crime Scene Investigation and Evidence Collection By the end of this chapter you will be able to:
Summarize Locard’s exchange principle
Identify four examples of trace evidence
Distinguish between direct and circumstantial evidence
Identify the type of professionals who are present at a crime scene
Describe how evidence from a crime scene is analyzed
All Rights Reserved South-Western / Cengage Learning © 2012, 2009
Forensic Science: Fundamentals & Investigations, Chapter 2

2. Chapter 2 Crime Scene Investigation and Evidence Collection By the end of this chapter you will be able to:
Summarize the three steps of a crime scene investigation
Explain the importance of securing the crime scene
Identify the methods by which a crime scene is documented
Demonstrate proper technique in collecting and packaging trace evidence
Forensic Science: Fundamentals & Investigations, Chapter 2

3. Observations in Forensics
Study situations
Find clues in ordinary details
Work backwards from the evidence to what led up to the crime
Be patient
Practice
Forensic Science: Fundamentals & Investigations, Chapter 1

4. What Forensic Scientists do
Its not like the television show…
Find, examine and evaluate evidence from a crime scene.
One key skill for this job is observation
They often act as expert witnesses for prosecution lawyers.
Specialists deal with certain types of evidence:
ballistics experts, textile experts, blood spatter experts, vehicle experts, forensic anthropologists (human bone experts)
Forensic Science: Fundamentals & Investigations, Chapter 1

5. What Forensic Scientists Do
The ability to solve a crime depends on observing all the evidence left at a crime scene
Analytical skills require PRACTICE
They must work backwards from the evidence to figure out what actually happened
This is called deductive reasoning
The Deadly Picnic Lab
Forensic Science: Fundamentals & Investigations, Chapter 1

6. Principle of Exchange
Established by Dr. Edmond Locard, the principle states:
When a person comes in contact with an object or another person, a cross-transfer of physical material can occur
Study of the material can determine the nature and duration of the transfer
Forensic Science: Fundamentals & Investigations, Chapter 2

7. Testimony by a witness about what that witness saw, heard, or did
Types of Evidence
Direct evidence
Testimony by a witness about what that witness saw, heard, or did
Forensic Science: Fundamentals & Investigations, Chapter 2

8. Types of Evidence Circumstantial evidence Physical evidence
also called Indirect
trace evidence
Physical evidence
e.g., fingerprints
Biological evidence
e.g., blood or hairs
Forensic Science: Fundamentals & Investigations, Chapter 2

9. Types of Evidence Explain why this would be or
would not be trace evidence
Forensic Science: Fundamentals & Investigations, Chapter 2

10. The Crime Scene Investigation Team
Who is at the crime scene?
Police and
District attorney (possibly)
Crime scene investigators
Medical examiners
Detectives
Specialists
Forensic Science: Fundamentals & Investigations, Chapter 2

11. The Seven S’s of Crime Scene Investigation
Secure the scene
Separate the witnesses
Scan the scene
Seeing the scene
Sketch the scene
Search for evidence
Secure the collected evidence
Forensic Science: Fundamentals & Investigations, Chapter 2

12. Crime-Scene Sketch Form
Forensic Science: Fundamentals & Investigations, Chapter 2

13. Crime-Scene Search Patterns
Forensic Science: Fundamentals & Investigations, Chapter 2

14. FIRST CRIME SCENE

15. WHAT YOU KNOW
A worker at a museum arrived at work at her normal time of 7 am. While walking to her office, she saw a body on the floor and signs of a disturbance. She was afraid to touch the body and called 911.
Police arrived to find the body of a white male wearing dark clothing, approximately 5’6” tall and 150 pounds. He showed signs of blunt trauma to the back of his head.

16. CONTINUED
The body was found in the library section of the museum. It contains ancient historical manuscripts worth thousands of dollars each. The museum worker showed police a location on the shelf where dozens of manuscripts were missing.
The building showed no signs of forced entry. The security system hadn’t been working for weeks. The worker found the door locked when she arrived.

17. YOUR TASK Scene secured by the police; then CSI’s were called in
Your group will LOCATE & PHOTOGRAPH evidence and SKETCH the crime scene
DO NOT touch any evidence—we aren’t collecting evidence today
Equipment: cameras, rulers, tape measures, sketch pads

18. ROLES Groups of 6 will get 8 minutes each at the crime scene
Focus on MAIN POINTS first! Prioritize!
Divide team into 3 roles:
2 Searchers
2 Photographers
2 Sketch Artists

19. SEARCHERS determine best search method (see p26 in textbook)
alert photographers and sketchers to key evidence
With remaining time, conduct search for trace evidence

20. PHOTOGRAPHERS Photograph overview of scene (p 25)
Prioritize main/obvious points: body, blood stains, patent (visible) footprints, etc.
be “on call” from searchers for smaller/other items of evidence
Each piece of evidence (smaller items):
Large view showing location in relation to scene
Close-up
Close-up with ruler for size reference

21. SKETCH ARTISTS both people sketch overview of entire area. Include:
Points of possible entry and exit
Furniture
Body
If time allows:
divide area in half between the 2 sketch artists
Show locations of smaller items of evidence on sketch on your half
Sketches are refined later

22. Forensic Science: Fundamentals & Investigations, Chapter 2

23. Packaging the evidence
Crease a clean paper and place evidence in the X position
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
Forensic Science: Fundamentals & Investigations, Chapter 2

24. Evidence ID Forms
Forensic Science: Fundamentals & Investigations, Chapter 2

25. Chain of Custody
Maintaining a chain of custody log is essential to present credible evidence in court
Forensic Science: Fundamentals & Investigations, Chapter 2

26. Chain of Custody (cont’d.)
Bag the evidence Add identification Seal it Sign it across the sealed edge
Sign over to a lab technician Open bag on non-sealed edge
Return items to the evidence bag Seal evidence bag in another bag Sign the evidence log
Forensic Science: Fundamentals & Investigations, Chapter 2

27. Analyze the Evidence
Facts result from collected evidence processed by the forensic lab
Lead detective aims to see how facts fit into the crime scenario
Forensic Science: Fundamentals & Investigations, Chapter 2

28. Analyze the Evidence Lab results can:
Show reliability of witness accounts
Establish the identity of suspects or victims
Show suspects to be innocent or link them with a scene or victim
Forensic Science: Fundamentals & Investigations, Chapter 2

29. Crime Scene Reconstruction
Crime scene reconstruction involves:
Forming a hypothesis of the sequence of events
From before the crime was committed through its commission
Forensic Science: Fundamentals & Investigations, Chapter 2

30. Staged Crime Scenes
When lab results don’t match up with the testimony of witnesses
Common examples:
Staging a fire—to cover bankruptcy
Staging a suicide—to cover a murder
Staging a burglary—to collect insurance money
Forensic Science: Fundamentals & Investigations, Chapter 2

31. Staged Crime Scenes Was the crime scene staged? Consider:
Does the type of wound match the weapon?
Could the wound be easily self-inflicted?
What were the mood and actions of the victim before the event?
What were the mood and actions of the suspect before the event?
Forensic Science: Fundamentals & Investigations, Chapter 2

32. Summary
Locard’s exchange principle:
Contact between people and objects can transfer material that can determine the nature and duration of the transfer
Evidence can be direct or indirect
Physical or biological traces
A crime scene investigation team consists of police, detectives, crime scene investigators, medical investigators, and specialists.
Forensic Science: Fundamentals & Investigations, Chapter 2

33. Summary
Investigations consist of recognizing, documenting, and collecting evidence.
First responding officers identify the extent of the crime scene, secure it, and segregate witnesses.
Crime scene investigators document the crime scene.
Evidence is collected, packaged, and labeled.
The evidence is analyzed and interpreted to fit the crime scenario.
Forensic Science: Fundamentals & Investigations, Chapter 2