Unit 3 - Physical Evidence & Evidence Collection

Evidence

Data on which a judgement or conclusion may be based

• Testimonial

• Documentary

• Demonstrative

• Physical

Testimonial Evidence

Info obtained through interviewing and interrogating indivuals about what they:

• Saw (eyewitness evidence)

• Heard (hear/say evidence) - doesn’t usually come into court

• Know (character evidence

Documentary Evidence

Written/electronic materials (including emails and text messages), audio recordings, videos 

Demonstrative evidence

Includes mock-ups and scale models of object or places related to the crime scene and helps juries visualize more clearly what they are unable to view personally

Physical Evidence

Anything real (tangible) that helps establish the facts of a case.

• Can be seen, touched, smelled, or tasted; is solid, semisolid, or liquid; can be large or small

• Can be at the scene, miles away or on a person

• Helps to provide new leads, tie one crime to another, and can corroborate (support) statements from victims and witnesses

Will only be admitted at trial if the legal rules have been followed from the crime scene to the courtroom 

Direct evidence

Establishes proof of a fact without any other evidence

• is a prima facie evidence - evidence established by law (blood alcohol level of .8% is evidence of intoxication in some states)

Indirect evidence (circumstantial evidence)

• Merely tends to incriminate a person

• Evidence from which inferences are drawn

Steps in evidence collection 

1.) Secure the scene

2.) Locate the evidence

3.) Document the evidence (may start before evidence is located)

4.) Collect and package the evidence

Number Placards

for items you plan to collect/remove from scene

Letters

for observation (something that you are noting or analyzing at the scene) 

• ex.) blood patterns, bullet holes, areas of damage, toolmark, footwear impressions

Chain of custody 

Chronological documentation of custody, transfer, analysis and storage of evidence

• Evidence must be strictly accounted for to avoid allegations of tampering, planting and cross-contamination

Cross-contamination 

Occurs when evidence from one item contacts and contaminates another piece of evidence.

• Destroys integrity, validity and credibility of evidence and its handlers.

• Based on Locard Exchange Principle: 

  • when something comes into contact with something else, there is an exchange.

Packaging procedures

1. Case/Incident number

2. Item number

3. Item description

4. Location collected from 

5. Initials of collector

6. Date

The Daubert standard

Expert testimony is reliable and relevant

4 Prongs

Testable, peer reviewed, established error rate, and generally accepted in scientific community

Statue of limitations

is the length of time evidence must be retained before disposal