Crime psych-2- collection and processing of forensic evidence

  • Created by: livvvx
  • Created on: 31-03-19 16:16

The collection and processing of forensic evidence (Biological)

Forensic evidence is info that is collected at a crime scene. This includes; blood splatter, shoe prints, tyre tracks, hair and fibre samples, fingerprints.

Issues with forensic evidence- Brandon Mayfield:

  • March 2004- terrorist-related bomb attacks on trains in Madrid. 191 people were killed and 1800 injured. An international investigation took place.
  • Using fingerprints found on a bag that was believed to belong to the bomber, the FBI suspected Brandon Mayfield, a muslim man who had been of interest to the FBI since the WTC attacks on 9/11.  A number of experts confirmed that it was his fingerprint.
  • However, the spanish police eventually found the real bomber, Ouhnane Daoud- an Algerian.
  • Mayfield was cleared and offered a formal apology from the US govt.

Hampikian et al (2011) conducted a review of trial transcrips and found that:

  • 35% of blood analysis evidence was incorrect
  • 22% of hair comparisons were incorrect
  • 3% of bite marks were incorrect
  • 2% of fingerprint analysis was incorrect

Many features can cause these errors in seemingly objective scientific methods such as; the seriousness of crime, observer bias, emotional impact, overconfidence, quality of evidence.

Dror (2012)- the evidence can be analysed by computers and machines but it in the end it is a human who has to make a judgement- and human error is what is responsible for the mistakes.


  • Fingerprints and ridge details- Fine patterns you see on the pads of fingers and thumbs. Each one is unique 
  • Fingermark (prints)/ latent mark- Fingers leave a trace of this pattern on surfaces we touch, latent mark is more general and can apply to the patterns of ridges left e.g. by palms or the soles of feet, these are often poor quality, incomplete, smudged, distoreted or obscured.
  • Comparison/inked prints- Marks can be used to determine whether they match the prints of a known suspect- taken in controlled conditions so they are high quality.

What is the job of a crime scene analyst?

Their job is to decide whether the ridge details on the suspect's finger(s) matched those fingermarks collected from the crime scene.

Why are two fingerprint experts needed to complete the identification process?

In order to verify the judments made and reduce likelihood of misidentifications.

Dror (2011) identifies 2 forms of inconsistencies that can exist when analysing fingerprints:

  • Inter-observer consistency (diffs between fingerprint examiners)
  • Intra-observer concsistency (diffs in one fingerprint examiner over time)

Motivating factors and bias in the processing of forensic evidence:

A cog bias is when someone is not accurate or objective about the way they think about something- fingerprint analysis. There are several types of cog bias that might influence whether a ''match'' is made or not.

  • Conformity effect= if asked to agree or disagree with other people (like a supervisor) the expert won't challenge a previous decision.
  • Need-determination perception= if there is a strong desire to solve a crime, the expert may suggest that they have identified a match for the fingerprints even when the more…


No comments have yet been made