1. 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 All Rights Reserved South-Western / Cengage Learning © 2009

2. 2 Crime Scene Investigation The goal of CSI is to recognize, document, and collect evidence at the scene of a crime Solving the crime will then depend on piecing together the evidence to form a picture of what happened at the crime scene

3. 3 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. Intensity, duration, and nature of the materials in contact determine the extent of the transfer.

4. 4 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.

5. 5 Types of Evidence Class evidence - narrows an identity to a group of persons or things. Individual evidence - narrows an identity to a single person or thing. –Has a unique combination of characteristic that could only belong to one person or thing

6. 6 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.

7. 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. 8 The Seven S’s of Crime Scene Investigation 1. Secure the scene. 2. Separate the witnesses. 3. Scan the scene. 4. See to it that the crime scene examiners receive overall and close up photos with and without measuring rulers. 5. Sketch the scene. 6. Search for evidence. 7. Secure the collected evidence.

9. 9 Securing the Scene Responsibility of first-responding police officer 1st priority - safety of individuals 2nd priority - preserving evidence Establish a perimeter - make it large Keep a security log of people at scene Limit “visitors” to essential personnel

10. 10 Separating the Witnesses Investigators will compare witness accounts Separation will prevent collusion - same story Each witness needs to be asked: –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?

11. 11 Scanning the Scene Done by forensic examiners Determine where photos should be taken Determination of: –Primary scene - robbery in front of a store –Secondary scene - home of suspect

12. 12 Seeing the Scene Crime scene examiner needs to see the scene Takes tons of pictures –Wide to tight –Include reference objects, any evidence, bodies

13. 13 Sketching the Scene Accurate, rough sketch of crime scene Note position of body, any evidence Objects should be measured from 2 immovable points North should be labeled and scale used included Any other objects in area: doors, windows, trees, cars, etc. More accurate sketch made court

14. 14 Searching for Evidence A spiral, grid, linear, or quadrant pattern should be walked and location of evidence marked, photographed, and sketched Also used: additional light sources and a vacuum cleaner

15. 15 Securing and Collecting Evidence All evidence needs to be properly packaged, sealed, and labeled Specific protocol depending on evidence –Liquids and arson remains in airtight containers –Biological evidence in breathable containers so it can dry out –Put in paper bindle, then in bag/container –Taped shut and signed by collector

16. 16 Securing and Collecting Evidence Evidence labels need to include: –Case number –Item inventory number –Description of evidence –Name of suspect –Name of victim –Date and time of recovery –Signature of person recovering the evidence –Signature of any witnesses present during collection

17. 17 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.

18. 18 Chain of Custody In order to present credible evidence in court, a chain of custody log is essential. 1. A person bags the evidence, marks it for identification, seals it, and signs it across the sealed edge (above, left). 2. It is signed over to a technician in a lab for analysis who opens it, but not on the sealed edge. 3. After analysis, the technician puts it back in the evidence bag, seals it in another bag, and signs the evidence log (above, right).

19. 19 Analyze the Evidence The facts of the case are determined when the forensic lab processes all the collected evidence. The lab then sends the results to the lead detective who aims to see how it all fits into the crime scenario.

20. 20 Analyze the Evidence The lab results 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.

21. 21 Crime Scene Reconstruction Crime scene reconstruction involves: –forming a hypothesis –of the sequence of events –from before the crime was committed –through its commission.

22. 22 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.

23. 23 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.

24. 24.......... Summary.................. 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. The investigation consists of recognizing, documenting, and collecting evidence.

25. 25................. Summary................. Summary First responding officers identify the extent of the crime scene, secure it, and segregate witnesses. Crime scene investigators document the crime scene. Evidence must be collected, packaged, and labeled. The evidence then is analyzed and interpreted to fit the crime scenario.