2. The collection and processing of forensic evidence Flashcards
Motives of fingerprint analysts interviewed:
- Rewards (job satisfaction linked to skills)
- Hope and satisfaction related to catching criminals and solving crimes;
- Factors linked to case importance (e.g. serious or long running cases);
- Feelings associated with searching for and finding matches;
- The need for closure on cases and fear about making mistakes.
Brandon Mayfield
A high profile case showed that finger print analysis is not as objective and full proof as both forensic scientists and the general public might believe. On the 11 March 2004 a series of bombs went off in a co-ordinated attack on 4 commuter trains in Madrid, Spain As result of these attacks, 191 people were killed and 1800 people were wounded.
A latent finger print which had been created by sweat was lifted from a bag believed to have belonged to the bomber and contained detonating devices. Using the standard FBI fingerprint analysis protocol, a suspect was identified.
He was a US suspect, an American Muslim called Brandon Mayfield, who had been a person of interest to the FBI since the 9/11 bombings. The FBI had a number of fingerprint experts examine the fingerprint. All agreed it was Mayfield’s. Mayfield, however, protested his innocence and asked, when he appeared in court, for an expert appointed by the defence to examine the fingerprint.
This was done and the expert also confirmed that the print was Mayfield’s. This evidence would surely have been key in the trial of Brandon Mayfield had it not been for the fact that the Spanish police matched the print to the real bomber, an Algerian national called Ouhnane Daoud.
The print was not Mayfield at all!
- Emotional motivation
- Job satisfaction
- Catching the criminal
- Need for closure
- Emotional involvement
- Some crimes involve more emotions – Dror
- Cognitive biases
- Contextual biases
- Confirmation biases
Cognitive biases
- Cognitive factors have been seen to influence finger print analysis as it is an information processing task and involves processes such as attention and visual searching.
- Contextual bias is where someone has other information aside from that being considered, which influences (either consciously or subconsciously) the outcome of the consideration. E.g. Details from the case
- Confirmation bias people test hypotheses by looking for confirming evidence rather than for potentially conflicting evidence. E.g. they have a suspect in mind so only look for supporting evidence rather than any anomalies
Background Research: Dror 05 - Method?
Lab experiment
Background Research: Dror 05 - Participants?
The participants in this study were 27 university student volunteers, with a mean age of 23 (nine were males and 18 were females).
Background Research: Dror 05 - Materials and apparatus?
Ninety-six pairs of fingerprints. 48 pairs of the fingerprints provided clear and detailed bottom-up information (unambiguous). 48 were unclear and much harder to come to a conclusion (ambiguous) which is more realistic.
Background Research: Dror 05 - Procedure - (3 major points with expansion)
- We invoked two emotional states
Low – descriptions of minor crimes with pictures of stolen items
High – descriptions of violent crimes with shocking pictures (e.g. knife wound to victims face). - Subliminal
To further increase the strength of our top-down bias to find a match we included subliminal messages (‘guilty’ and ‘same’ messages flashed up before the fingerprints) - All participants completed all conditions on a PC
Background Research: Dror 05 - Results: guilty?
Background Research: Dror 05 - Conclusion (2)
- When prints are ambiguous, emotional context can influence the likelihood of matching of fingerprints.
- When bottom up information (the details of the fingerprints) is unclear, top down processing (the beliefs/mental state) of the individual have more impact on decision making.
