CJ II / Physical Evidence Skills USA

What is Physical Evidence? The definition depends somewhat on who you ask. PE consists of objects and things: –Can be very large –Microscopically small PE could be everything and anything depending on the crime and circumstances.

Physical Evidence vs. Verbal Testimony – Eye Witness Which do you think is better? Advantages of Physical Evidence: –Doesn’t lie; it is what it is –Doesn’t forget –Doesn’t get confused –Doesn’t die or move away –No bias or prejudice

Locard’s Principle of Exchange Stated simply: every contact leaves its trace –Every contact between people and/or objects will result in the exchange of evidence of the contact.

Role of Physical Evidence What can it do? Defining the element of the crime - Proof that a crime has been committed. Providing investigative leads for a case. –Example: Identification of a vehicle type in a hit- and-run case through automotive paint & glass analysis.

Role of Physical Evidence -continued- Linking a crime scene or a victim to a suspect. –Examples: hair, blood, semen, fingerprints Corroborates or refutes a suspect’s statement or alibi.

Role of Physical Evidence -continued- Identifying a suspect - the identification of a suspect is not limited to but often established through fingerprint comparison or DNA profiling. Inducing a confession of a suspect - presenting factual information to a suspect may encourage the person to admit involvement in a crime. Exonerating the innocent - PE may be found that proves a person did not commit a crime.

Role of Physical Evidence -continued- Reconstruction of a crime. –Example: A rape-homicide victim is found discarded in the woods. The victim is covered with blood. Located in the suspect’s bedroom are medium velocity impact blood spatter. The blood stain tested has the identical genetic markers as the victim. This information indicates the victim was assaulted at one point in time in the suspect’s bedroom.

Role of Physical Evidence -continued- Information on the Modus Operandi- many criminals have a particular modus operandi (method of operation, or MO) which consists of their personal characteristic way of committing a crime. –Examples: Type of accelerant and the way in which fires are set (“signature” of the arsonist) Sexual assault-approach, conversation, specific acts

Roles of Physical Evidence -continued- Providing expert testimony in court- presentation of PE in court by an expert is the ultimate test of the validity of the evidence. “CSI Effect”- juries expect physical evidence.

Class vs. Individual Evidence Class evidence: –Compared with a group –Could have several possible sources Individual evidence: –Compare the item with a specific object or person and include or exclude it as having originating from it –Unique-from only one source

Class vs. Individual Evidence -continued- Class evidence examples: –Soils –Fibers & hairs (if no DNA) –Fire residues Individual evidence examples: –Fingerprints –Bullets & casings –Shoe & tire impressions

Mechanical fit AKA “fracture matching” Is a unique form of evidence Mechanical fit is where an item is damaged and pieces are deposited in the scene Because the breakage is accidental, it is also random which makes it individual –Example: –Piece of broken headlight lens left at the hit-and-run scene compared to the suspect vehicle with a partially broken headlight.

There are three major steps in the process of evidence collection.

1. Recognition of Evidence Recognition: takes a thorough knowledge of what is likely to be present at a crime scene of a given type of crime. –What types of evidence are inherent at a given type of crime? Before evidence is collected, its exact location must be recorded by: –Photographs (and video) –Diagrams (with measurements) –Systematic, detailed note taking

2. Collection of Evidence Collection: How much evidence should be collected? –As much as possible…there is no such thing as too much evidence! Be aware of “cross contamination” –Directly associated with Locard’s Principle of Exchange –Caused by inappropriate handling of evidence Especially trace and serology evidence

3. Packaging and Preserving Evidence Once the evidence has been located and collected, it must be properly packaged. There are: –Physical –Scientific, and, –Legal requirements that determine how evidence should be packaged Evidence bags must have proper ID info. printed on them. Evidence bags must be sealable and opened only by Lab. Personnel or the CSI/Officer.

3. Packaging and Preserving Evidence -continued- Packaging for evidence must be designed to preserve the evidence to the maximum extent possible. Different types of evidence require unique packaging to preserve it –Consider how would you package the following items. Living plants (marijuana) Wet blood or body fluids Dry blood or body fluids Trace evidence such as hairs, fibers, small paint chips, or glass

3. Packaging and Preserving Evidence -continued- Collection Examples: Dry Blood – wet swab collection Wet Blood – dry swab collection Hair fibers – collect w/tweezers Pistol – unloaded & chamber open DNA collection – dry swab of mouth Plastic bags vs. Paper bags

Basic Evidence Collection Kit

Chain of Custody #1 reason why physical evidence is inadmissible in court! Rules of evidence in every federal and state court requires that all evidence is authenticated. –This means there must be a record of who is in possession of the evidence from the time it is collected at the crime scene until the time it gets to court.

Chain of Custody -continued- The evidence must also be: –Uniquely identified in such a way so that it cannot be confused with any other piece of evidence. –Must prove the evidence in court is the same evidence that was collected at the crime scene. –Evidence must be packaged in tamper-evident packaging w/proper labeling. If there is a break in the Chain of Custody, the evidence will not be allowed in court!

In closing…. A crime scene has a story to tell, and the evidence at the scene helps tell the story. Each piece of evidence will contribute to the story. Once the evidence has been collected and analyzed, the “CSI” should be able to reconstruct what happened.

Questions?

Physical Evidence - Summary PE could be everything and anything depending on the crime and circumstances. Role of Physical Evidence: Defining the element of the crime. Proof that a crime has been committed Providing investigative leads for a case Linking a crime scene or a victim to a suspect Corroborating or refuting a suspect’s statement or alibi Identifying a suspect Exonerating the innocent Reconstruction of a crime Information on the Modus Operandi Providing expert testimony in court Class vs. Individual Evidence Collection of Evidence Chain of Custody