Criminal Topic 2- Collection And Processing Of Evidence (bio) Flashcards
What is topic 2
The collection and processing of forensic evidence
What is the research in topic 2
Key: hall and player supporting: dror, dror top down bias, lsu and Miller
Outline key research by hall and player
Background: from drors research p- fingerprint identification decreases and is effected by top down processes but done on undergrad students so wanted to test on experts. Aims: does a written report of the crime effect fingerprint experts id of poor quality print, are experts emotionally affected by circumstances of a case. Method: 70 volunteer fingerprint experts working for metropolitan police fingerprint bureau. Experience >3months-30+years, most active some managerial, all responded to a request. Materials: f.p from known source used, print scanned onto computer and superimposed onto corner of 50 pound note (detail obscuring ridge detail) 14 prints were made and compared for consistency and shown to sample of practitioners to confirm ambiguity). Each p given 1/14 f.p, suspects prints, crime scene examiners report, the context. Procedure: all ps took part and part of normal working day, tested in typical analyst room in new Scotland Yard f.p bureau, each given access to magnifying goaded and Russell comparator, told to act as normal , come and go but not discuss, each anonymous. Half assigned to low emotional context (report referring to allegation of forgery) and half to high emotional context (murder ‘suspect fired 2 shots’). Ps filled in experience, presented in court, where worked and asked to decide if mark was 1. Identification (match) 2. Not identification 3. Insufficient (not enough detail to make comparison) 4. Insufficient detail to tell identity, asked if referred to crime scene. Results: 57/70 said read cs report (30high) 52% of 30 said they believed it influenced their decision/6% in low. Found no sig diff between high and low. No. Experts identified were 6 in high, 7 in low. No match was 1 in high, 0 in low, insufficient was 15 high, 12 low. Conc: context doesn’t affect experts ability
Dror-top down bias
When analysing f.p 2 approaches take place: 1. Bottom up: use of examination of ridges and patterns to identify unique features but if prints degraded then must use 2. Top down approach: use experts previous experience and knowledge of make assumption. Top down open to more mistakes/bias. Observer/expectancy, selective attention, conformity bias (won’t challenged another’s opinion if asked), need determination (when strong desire to solve crime), overconfidence (due to experience) confirmation bias (confirming what you think you know)
Dror et al-research with 27 students
27 uni student volunteers (9m,18f) mean age 23. 96pairs of f.p, half obvious bottom up so easy match and half more ambiguous so follow top down process. Two emotional states, low (bike theft/burglary) and high (murder and personal attacks) with photos to reinforce context. Subliminal condition: words same or guilty flashed w info. Ps pressed button for same or diff after each pair. % matches found for ambiguous prints control:47, low 49, high 58, high and subliminal 66. In unambiguous, unaffected by emotional states as bottom up
Linear sequential unmasking (lsu)
Normally work in a circular line of reasoning (evidence then case details) but linear works from evidence to suspect, preventing confirmation bias. Expert must first examine and document evidence before exposed to reference material. Following initial analysis of trace evidence, sequential unmasking ensures case info presented later and only when necessary in sequence of importance . Expert can revisit analysis but not make changes, only add and say how confident
Miller-six pack
Suggested the line up method to reduce the amount of false positives (misidentification). Gave students either one hair sample of 5 to match evidence to suspect. Means instead of looking for a match you are more likely to say no if unsure (discount other suspects rather than forced choice)
Strategy for reducing bias in collection and processing of evidence
Don’t read crime report, use lsu, undertake extra training
