Forensic Evidence Flashcards
What could make a difference in the way you see evidence ?
- Emotional reaction:
- Nature of the crime
- Characteristics of the victim
- Personal bias of the expert
- Physical or psychological harm to the victim
- Age of the victim
- Use of a weapon
What are the 3 basic fingerprint classes ?
-Arches
-Loops
-Whorls
=based on visual pattern
What are Arches ?
- Plain and Tented arches
- Plain- formed by ridges that enter on one side of the print and exit on the other
- No deltas are present
- Tented- spike in the middle
What are Loops ?
- One delta
- One or more ridges that enter and leave on the same side
- Radial and Ulnar Loops
What are Whorls ?
- At least one ridge that makes a complete circuit
- 2 deltas
- Double loop= 2 loops combined into one whorl
- Accidental whorl= two or more patterns
What errors occur in collecting fingerprints ?
- Human expert makes final decision on whether its a match (objective)
- Led to errors with fingerprints, blood evidence, hair comparisons and bite marks
- Confirmation Bias- Give extra emphasis to evidence which supports their current beliefs
- Different patterns can distort perception
What did Dror (2011) find out ?
-Different fingerprint examiners differ from one another and themselves over time
What were Dror’s discoveries linked to ?
- Cognitive factors/biasing decisions- comparing fingerprints involves information processing tasks (attention/visual searching)
- Clarity of fingerprint decreases=decision is more subjective (easy to see shapes that aren’t there)
- Emotional context- context and pressure of crime scene
- Decisions in a highly emotional context, increases chance of a match being made with an unclear print
What motivating factors did Dror find in collecting fingerprints?
- Need to solve crime
- Maintain their reputations
- Can affect decision making
What were the Aim of Hall and Players study ?
- Whether fingerprint examiners are emotionally affected by the case details in a report
- See if emotional context would bias their judgements
What was Hall and Player’s sample ?
- 70 fingerprint experts
- Working for Met Police in London
- Mean of 11 years experience
- Most dealt with crimes from burglary to terrorism
- Self selected sample
- Data was anonymous
How was the fingerprint created in Hall and Player’s study ?
- Made from known source
- Scanned and superimposed onto an image of a £50 note (only just identifiable)
- Other experts confirmed the mark was poor quality and unclear
What was the procedure that the experts followed in Hall and Player’s study ?
- Each expert given a test mark card, set of 10 prints and scene examiners report
- Typical case report, but told which finger print was from to save time
- Independent measures design
What controls were there in Hall and Player’s study ?
- Each given magnifying glass and optical magnifier to compare images
- Told to treat it like an ordinary day
- Spoke to each other, just not about the fingerprints
- No time limit
What were the two conditions in Hall and Player’s Study?
- Low Emotion- crime was a forgery
- Fake £50 note
- High Emotion- crime was a murder
- Shot the cashier when the note was turned down
- Otherwise the reports were the exact same, apart from what happened to the cashier in high context
