Evidence Collection and Preservation

Chain of custody

Crime scene -> evidence room -> crime lab –> courtroom 

• If you can’t maintain this, you can’t testify in court  

• You must always legally obtain evidence, you need a warrant  

• If it’s illegal, you will be squashed in court and all that work will be pointless 

What is evidence?

•  something legally submitted to a competent tribunal as a means of ascertaining the truth of any alleged matter of fact under investigation before it (physical, real evidence, not testimonial evidence)  

• Has to be legal in your crime scene (legal search)  

• 4^th amendment  

• 1) Search warrant  

• 2) Consent (verbal or written) (however verbal can lead to problems, he said she said, so it’s best to have written) (never assume consent) 

• 3) Emergency/exigent circumstances  

• Ascertaining the truth – to inform the judge or jury  

• Alleged matter of fact – about an issue they are making a decision about  

• Competent tribunal – court of law  

What can evidence do?

• Think evidence overall and not just at a crime scene 

• 1) Prove that a crime has been committed or establish key elements of a crime 

• 2) Can place a suspect in contact with the victim or the crime scene  

• Locard’s transference principle  

• 3) can establish the identity of persons associated with the crimes 

• Identity v. individualization 

• 4) physical evidence can exonerate the innocence 

• 5) can corroborate the victim’s testimony 

• 6) a suspect confronted with evidence may make admissions or even confess  

• 7) physical evidence may be more reliable than eyewitnesses to the crime 

• The Norfolk 4 – cognitive dissonance: the mental discomfort that results from holding two conflicting beliefs, values, or attitudes 

• 8) court decisions have made physical evidence more important  

• Miranda – limit the authority of the police to rely on statements and confessions made by defendant 

• 9) juries expect physical evidence 

• CSI effect 

• Explain everything  

• 10) negative evidence – the absence of physical evidence may provide useful information 

• Absence of evidence is not evidence of absence

Assessment of a scene

• Walk through – assessing the scene for anything out of place (creating a story line or hypothesis of what happened)  

• Observe and collect evidence (make connections)  

• Reconstruction (scene <-> victim <-> perpetrator) 

• Context  

• Identity – who are the “players”   

Observe

• Preliminary hypothesis about what happened 

• Prove and disprove 

• Generate questions 

• Physical evidence answers questions  

What’s not there

• Causation by elimination  

• Circumstances surrounding 

• Medical records 

• Medications 

• Social history  

• Identify 

• What is evidence? 

• Document 

• Photo 

• Diagram 

• Collect 

• WSCL evidence collection book 

• Preserve  

• Evidence room 

major themes- collection and preservation of evidence

 

• Proper handling of physical evidence  

• Proper techniques of collection (WSCL manual) 

• Proper techniques of preservation  

• Legal issues concerning collection and preservation  

• 4^th amendment search and seizure 

• Laws constantly change  

• Evidence integrity 

• Chain of custody 

• Storage issues 

• Cannot be tampered with  

• What should be collected? 

• What does the lab need collected to do their analysis? 

why collect evidence

• 1960s the President’s Crime Commission Task Force reports on Police and Science and Technology (1967) called for greater reliance on physical evidence in the investigation and adjudication of crimes  

• Forensic laboratories have multiplied almost four-fold since the early 1970s 

• Studies in the 1960s and 1970s indicated physical evidence was available at most crime scenes, but little scientific evidence was collected and had minimal impact on case outcome  

• Peterson et al. (1984) found clearance rates of offenses with evidence scientifically analyzed were about three times greater than in cases where such evidence was not used 

• Briody (2004) found homicide cases with DNA evidence were much more likely to reach court and had a positive effect on juries’ decisions to convict 

forensic evidence and the police (Peterson, et al., 1984)

• Physical evidence was collected and analyzed in only 20-30% of all serious crimes 

• 100% of murder and drug cases 

• 75% of rape cases 

• Only 10-20% of attempted murders  

• 33% of burglaries 

• 20% of robberies 

• Clearance rates of offenses with evidence scientifically analyzed were about three times greater   

• Roman et al.  

locard’s exchange principle

when a person comes into contact with an object or another person, a cross transfer of physical evidence can occur