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
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
describe how evidence from a crime scene is analyzed
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Forensic Science: Fundamentals & Investigations, Chapter 2

2. 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:
When a person comes in contact with an object or another person, a cross-transfer of physical material can occur.
Evidence can be found on both persons (and/or) objects because of this cross-transfer.
Study of the material can determine the nature and duration of the transfer.
The intensity, duration, and nature of the materials in contact determine the extent of the transfer.
More transfer would be noted if two individuals engaged in a fistfight that if a person simply brushed past another person.
Forensic Science: Fundamentals & Investigations, Chapter 2

3. Principle of Exchange (cont.)
Typical items that are transferred:
Hair, skin cells, clothing fibers, pollen, glass fragments, debris from a person’s clothing, or makeup.
These transferred materials are considered to be trace evidence.
small but measurable amounts of physical or biological material found at a crime scene
Forensic Science: Fundamentals & Investigations, Chapter 2

4. Examples of Trace Evidence
Pet hair on your clothes or rugs
Hair on your brush
Fingerprints on a glass
Soil tracked into your house on your shoes
A drop of blood on a T-shirt
A used facial tissue
Paint chips
Broken glass
A fiber from clothing
Forensic Science: Fundamentals & Investigations, Chapter 2

5. 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.
Forensic Science: Fundamentals & Investigations, Chapter 2

6. Types of Evidence
Direct evidence- evidence that (if true) proves an alleged fact, such as an eyewitness account of a crime.
-Examples: eyewitness accounts, police dashboard video cameras, confessions to a crime.
Circumstantial evidence- (indirect evidence) evidence used to imply a fact but not prove it directly.
- May provide a link between a crime scene and a suspect.
Trace evidence is a type of circumstantial evidence.
Can either be physical or biological
Physical evidence includes impressions such as fingerprints, footprints, shoe prints, tire impressions, and tool marks.
Biological evidence includes body fluids, hair, plant parts, and natural fibers.

7. Types of Evidence
Class evidence- material that connects an individual or thing to a certain group (see individual evidence).
Narrows an identity to a group of persons or things.
Individual evidence- a kind of evidence that identifies a particular person or thing.
Narrows an identity to a single person or thing. Example: fingerprints
Forensic Science: Fundamentals & Investigations, Chapter 2

8. Types of Evidence
Evidence taken from a crime scene. Direct or circumstantial evidence? Physical or biological evidence? Class or individual evidence? Explain why this would be or would not be trace evidence.
Forensic Science: Fundamentals & Investigations, Chapter 2

9. The Crime Scene Investigation Team
Police and possibly a district attorney.
Police are usually the first to arrive at a crime scene. The district attorney may be present to determine if a search warrant is needed.
Crime scene investigators.
Document the crime scene in detail and collect physical evidence.
Include recorders to record the data, sketch artists to sketch the scene, photographers, and evidence collectors.
Medical examiners.
To determine the cause of death
Detectives.
Look for leads by interviewing the witnesses and talking to the CSI about the evidence.
Specialists.
Entomologists, forensic scientists, forensic psychologists may be consulted.
Forensic Science: Fundamentals & Investigations, Chapter 2

10. The Seven S’s of Crime Scene Investigation
Secure the scene.
Separate the witnesses.
Scan the scene.
See to it that the crime scene examiners receive overall and close up photos with and without measuring rulers.
Sketch the scene.
Search for evidence.
Secure the collected evidence.
Forensic Science: Fundamentals & Investigations, Chapter 2

11. Securing the Scene Responsibility of the first responder.
The first police officer to arrive at a crime scene.
The safety of all individuals in the area is top priority.
Preservation of the evidence is second priority.
Begins to keep a security log of all those who visit the crime scene.
Forensic Science: Fundamentals & Investigations, Chapter 2

12. Separating the Witnesses
Witnesses must not be allowed to talk to each other because their accounts of what happened will be compared.
This is done to prevent collusion.
Questions asked of each witness:
When did the crime occur?
Who called in the crime?
Who is the victim?
Can the perpetrator be identified?
What did you see happen?
Where were you when you observed the crime scene?
Forensic Science: Fundamentals & Investigations, Chapter 2

13. Scanning the Scene
Forensic examiners need to scan the scene to determine where photos should be taken.
Primary crime scene- the location where the crime took place.
Secondary crime scene- a location other than the primary crime scene, but that is in some way related to the crime, where evidence is found.
A murder may have taken place in one location (primary)and the corpse found at another (secondary).
Forensic Science: Fundamentals & Investigations, Chapter 2

14. Seeing the Scene
Photos of the overall area and close-up photos with and without a measuring ruler should be taken.
Triangulation of stationary objects should be included in the photos as reference points.
A view of the crime scene should be taken from several different angles and distances.
Several close-up photos of any evidence and bodies should be taken.
Forensic Science: Fundamentals & Investigations, Chapter 2

15. Sketching the Scene
An accurate rough sketch of the crime scene is made, noting the position of the body (if any) and any other evidence.
All objects should be measured from two immovable landmarks.
On the sketch, north should be labeled and a scale of distance should be provided.
If the crime scene is outdoors, the position of trees, vehicles, hedges, and other structures should be included in the sketch.
Any other objects in the vicinity of the crime scene should be included in the sketch.
Include doors, windows, and furniture.
Later, a more accurate sketch will need to be made for possible presentation in court.
Forensic Science: Fundamentals & Investigations, Chapter 2

16. Searching for Evidence
Forensic Science: Fundamentals & Investigations, Chapter 2

17. Searching for Evidence
Forensic Science: Fundamentals & Investigations, Chapter 2

18. Searching for Evidence
Forensic Science: Fundamentals & Investigations, Chapter 2

19. Searching for Evidence
Depending on the number of investigators, a spiral, grid, linear, or quadrant pattern should be walked and location of evidence marked, photographed, and sketched.
Single investigators might use a grid, linear, or spiral pattern.
A group of investigators might use a linear, zone, or quadrant pattern.
Forensic Science: Fundamentals & Investigations, Chapter 2

20. Securing and Collecting Evidence
All evidence needs to be properly packaged, sealed, and labeled.
Packaged in a paper bindle.
a folded paper used to hold trace evidence.
Bindle is placed in a plastic or paper container.
The outer container is sealed with tape and labeled with the signature of the collector written across the tape.
An evidence log and a chain of custody document must be attached to the evidence container.
Chain of custody: the documented and unbroken transfer of evidence.
Forensic Science: Fundamentals & Investigations, Chapter 2

21. Packaging the 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.
Forensic Science: Fundamentals & Investigations, Chapter 2

22. Packaging the Evidence
There are standards for collecting different types of evidence that describe how to collect and store the evidence. Published by the FBI and state police agencies.
Control samples must be obtained from the victim for the purpose of exclusion.
Forensic Science: Fundamentals & Investigations, Chapter 2

23. Packaging the Evidence
Choose the appropriate-size sheet of clean paper for the bindle.
Crease the paper as shown.
Place evidence in the X location.
Fold left and right sides in.
Fold in the top and bottom.
Insert the top flap into the bottom flap then tape closed.
Place the bindle inside a plastic or paper evidence bag. Fold the bag closed.
Place a seal over the folded edge of the evidence bag.
Have the collector write his/her name over the folded edge.
Forensic Science: Fundamentals & Investigations, Chapter 2

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 (above, left).
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).
Ensures that the evidence has been responsibly handled as it was passed from the crime scene to a courtroom.
Forensic Science: Fundamentals & Investigations, Chapter 2

25. Analyze the Evidence
The facts of the case are determined when the forensic lab processes all the collected evidence.
Evidence is examined and compared with the witnesses’ statements to determine the reliability of their accounts.
The lab then sends the results to the lead detective who aims to see how it all fits into the crime scenario.
Leads to crime scene reconstruction; forming a hypothesis of the sequence of events from before the crime was committed through commission.
Forensic Science: Fundamentals & Investigations, Chapter 2

26. Analyze the Evidence The lab results (evidence analysis) can:
Show how reliable are any witness accounts.
Establish the identity of suspects or victims.
Show suspects to be innocent or link them with a scene or victim.
Confirm verbal witness testimony.
Acquit the innocent.
Forensic Science: Fundamentals & Investigations, Chapter 2

27. Crime Scene Reconstruction
Crime scene reconstruction involves:
forming a hypothesis
the sequence of events
The time before the crime was committed
and through its commission.
Forensic Science: Fundamentals & Investigations, Chapter 2

28. Staged Crime Scenes
When the lab results do not match up with the testimony of witnesses, it can mean the crime was staged; common examples include:
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

29. Staged Crime Scenes
1. Treat all death investigations as homicides. 2. Do the types of wounds found on the victim match the weapon? 3. Could the wounds be easily self-inflicted? 4. Establish a profile of the victim through interviews with friends and family. 5. Evaluate the behavior (mood and actions) of the victim before the event. 6. Evaluate the behavior (mood and actions) of any suspects before the event. 7. Corroborate statements with evidential facts. 8. Reconstruct the event. 9. Conduct all forensic examinations to determine the facts of the case.
Forensic Science: Fundamentals & Investigations, Chapter 2

30. Staged Crime Scenes
To help determine whether a crime scene was staged, consider:
Whether the type of wound found on the victim matches the weapon employed.
Whether the wound could have been easily self-inflicted.
The mood and actions of the victim before the event.
The mood and actions of a suspect before the event.
Forensic Science: Fundamentals & Investigations, Chapter 2