Background: Collecting and Processing Forensic Evidence

• Why is finger print testing widely used?

  It is time and cost effective and relatively easy to analyse. No two people have yet been found to have the same fingerprint yet.
• How are fingerprints checked?

  On a database with many stored fingerprints (of people with previous convictions) which can be done for a rapid search for a match of the print lifted from the crime scene.
• What trace body parts contain DNA which if often tested?

  Hair, blood, saliva, fingerprints and nails.
• Why is this unscientific?

  Human analysis is subjective so not quantitative.

  Fingerprint identification relies on pattern matching followed by detection of certain ridge characteristics e.g. lakes, ridge endings
• What are the four types of bias?

  Conformity bias, Expectancy bias, Motivational bias, Cognitive/perceptual bias.
• What is conformity bias?

  When one expert says there's a match, the other experts expect this to be right and agree to conform to majority.
• What is expectancy bias?

  When expert is aware of characteristics of suspect, their expectations may bias whether they believe it's a match
• What is a motivational/emotional bias?

  When a case is highly emotional e.g. involves a victim, experts are more motivated to find a match.
• What is cognitive/perceptual bias?

  Each expert may have individual differences in their perceptions- cognitive functions-see ridge details that aren't there.
• What are other problems with using fingerprint analysis?

  1. could be multiple prints left at a crime scene- hard to figure out which latent prints should be compared to known prints
  2. latent prints left at scene may be poor quality/unclear
  3. prints may be stored in database e.g. in suspect has no prior convictions
  4. lots of biases when deciding if prints are a match e.g. confirmation bias, emotional bias
• What is latent print?

  Print found at scene
• What is the known print?

  One collected from a suspect/in a database
• What did Dror research?

  Whether decisions about fingerprints in a highly emotional context increases the likelihood of a match decision when being made with an ambiguous decision.
• What sample did Dror use?

  University students who volunteered
• What did Dror's research involve?

  Students given either good quality or poor quality fingerprint to study. Also given emotional stimuli aka a case file was either low context (theft) or high context (murder) in murder case given disturbing photographic images of the victim. Results showed volunteers were affected by the emotional context and this interfered with their decisions, making them more likely to make matches or identification when analysing poor quality or ambiguous pairs of fingerprints. They were more motivated due to emotion bias.
• What is a limitation of Dror's research?

  Low population validity as fails to reflect target population of real experts who are trained to examine highly emotional cases and may be more impartial or skilled at recognising matches.