1. Crime Scene Investigation
Chapter 2

2. THE CRIME SCENE
CSI’s carefully and systematically sift through a crime scene in order to learn:
How and when the crime was committed
Who committed it and why
What items may have been removed from a crime scene
The methods used by anthropologists, archaeologists, and historians are similar to those used at a crime scene

4. THE CRIME SCENE (2)
There must be a plan for systematically searching the site
Safety of the searchers must be considered
Only highly qualified and trained people should conduct the search
Contamination must be minimized
Time may be of the essence
The scene must be thoroughly documented
There must be a chain of custody for each piece of evidence

6. A Crime Occurs & Is Discovered
Crimes can be discovered in one of three ways
A witness sees it and reports it to the police
A victim of the crime reports it to the police
The police discover the crime in progress
Police may also “discover” a crime with a sting operation
A scenario whereby criminals are encouraged to commit crimes that they probably would have done anyway

8. The First Officer at the Crime Scene
Determine if the perpetrator is still there
Hot search (immediate) or cold search (interview witnesses)
Tend to the injured
Secure the scene to prevent contamination
Do not walk through the scene and search for evidence
Note any obvious safety hazards and warn others

10. Crime Scene Investigation
After a crime scene has been discovered and protected, CSI’s will arrive
If there is a dead body, a forensic pathologist will
Certify the death
Determine the postmortem interval (PMI)
Take photographs and collect trace evidence
The CSI unit takes charge of the scene
Each member has a defined role:
Sketcher, photographer, searcher, documenter, fingerprinter, blood spatter analysis, etc.

12. Preliminary Scene Examination
The first duty of the CSI at a crime scene is to conduct a preliminary examination
Safety hazards must be addressed and remediated
Boundaries of the crime scene must be ascertained
Perpetrators often carry evidence away and there may one or more secondary crime scenes

14. Systematic Search of the Scene
Must be carried out in a way that minimizes alteration of the scene
Photograph as early as possible
Determine the search pattern that will be used
If it is a room, a spiral or back-and-fourth pattern may be used
Outdoor scenes are often divided into grids
Avoid covering the same ground more than once to minimize contamination

16. Recording the Crime Scene
Two basic methods
Freehand sketch including measurements of various objects – later translated into a scale drawing
Still photography including many pictures at different distances and angles under various lighting conditions
Hand drawn sketches are still used, but computers are often used to create scale drawings
Crime scenes are often videotaped

18. Collection of Evidence
Evidence is of little or no value if it is contaminated or degraded
At some crime scenes (especially homicides) forensic scientists work with CSI’s to process evidence
There are three major steps in the process of evidence collection
Recognition
Collection
Packaging/preservation

19. Recognition of Evidence
How do investigators know what is evidence and what is not?
Homicides, burglaries, sexual assaults and other crimes usually have some characteristic types of evidence
Weapons, blood, fibers, hair, fingerprints, tools, glass, soil, body fluids
There is no such thing as too much evidence
The exact location of the evidence must be recorded

21. Collection As much evidence as possible should be collected
Lack of sample size may limit testing
The defendant is given a chance to have their own tests performed, so if it is used up, it is excluded from trial
Probative value (significance of evidence) is greatly enhanced if it can be linked to a known material or object

22. Packaging & Preserving Evidence
There are physical, scientific, and legal requirements that determine how evidence should be packaged
All evidence must be authenticated
Chain of custody
Uniquely identified to avoid confusion with other evidence
Tamper-evident packaging must be used

24. Preserving Evidence
Packaging must be designed to preserve the evidence
It may be weeks or months before the evidence is analyzed
Different types of evidence require unique packaging to preserve it
Living plants, wet blood or body fluids, wet paint, trace evidence, powder, fire residue

26. Reconstruction
Once evidence is collected and analyzed, investigators will attempt to reconstruct the crime
Identities of the victims
Identities of the perpetrators
The sequence of events that took place
The focus is to link the suspect to the crime and build a case that will stand up in court beyond a reasonable doubt