Collection + Processing Of Forensic Evidence (biological) Flashcards
what does forensic evidence refer to
- Fingerprints
- DNA evidence from hair, skin cells etc.
- Bite marks
- Blood spatter analysis
- Evidence from computer hard drives etc.
- Evidence from footprints or tyre prints
- Fibres from clothing etc.
- Ballistics
refers to any evidence that is collected from sources other than
self-report from a victim, perpetrator or witness.
collection of evidence
All forensic evidence can still be subject to bias. Fingerprint analysis (which have been used at crime scenes for over 100 years) have been shown to be affected by this bias, particularly following the high profile case of Brandon Mayfield.
Hampikan et al. (2011)
Hampikan et al. (2011) reviewed transcripts of a number of wrongful
convictions and found that forensic evidence was involved variety of ways:
- 38% contained incorrect blood analysis
- 22% contained incorrect hair comparisons
- 3% contained incorrect bite mark identifications
- 2% contained incorrect fingerprint identifications
Motivating factors and bias in the collection
- Charlton et al (2010) interviewed 13 fingerprint analysts and produced and in-depth description of their main motives. They summarised them as:
- Rewards (job satisfaction linked to skills)
- Hope and Satisfaction linked to catching the criminal and solving the case
- Factors linked to case importance (seriousness and length of time passed)
- Feelings associated with searching for and finding matches
- The need for closure
- Fear about making mistakes.
Dror et al. (2011)
- 2 analysts used when analysing fingerprints to prevent bias as they are usually unclear when collected.
- Dror et al. (2011) found discrepancies between analysts when looking at same finger prints, + also when 1 analyst looked at same finger prints on multiple occasions (low intra- rater and inter-rater reliability)
- One reason for this, is range of cognitive factors which can bias decisions.
- Comparing fingerprints is an information-processing task + involves processes such as attention and visual searching. Pertinent information could sometimes draw a persons attention and irrelevant information could distract them.
- Attention and emotion may cause interpretation changes
- As finger mark clarity decreases interpretation can become more
difficult and subjective and therefore open to bias. - Instead of relying on tested scientific methods, the process is mostly based on the subjective beliefs of the analyst, and if there is pressure to find an offender, errors are more likely to occur.
what factors effect bias
- The type of crime
- The nature of the victim
- The nature of the suspect
- The type of photos included in the file
problems with fingerprint analysis
Subjective contours can distort data so we can think we see things which aren’t there. Thus, a fingerprint analyst may see a contour or ridge which actually isn’t there, especially if actively trying to find point of match.
There is some evidence that experience may help, but even those who are most experienced can still have issues as a result of “circular reasoning” – that once some points of similarity are found, others are then “found” (imagined) to support them.
hall + player aim
In the UK fingerprint examiners are provided with a copy of the crime scene report, (which details the nature of the crime)
- Hall and Player thought it was important to determine if these practices introduce an emotional bias:
The study aimed to investigate whether:
> Fingerprint experts were emotionally affected by the case details?
> Does emotional context bias the judgements of expert analysts
hall + player sample
- 70 participants, all working for the Metropolitan police fingerprint bureau, responded to a request for volunteers to take part in an experiment. The request did not give details of the experiment.
- Their length of experience as experts ranged from less than three months to over 30 years. The mean length of experience was 11 years.
- 12 had managerial roles and although were still on the UK National Register of fingerprint experts, they were no longer active practitioners.
further sample
- To make sure the experts decision was accurate a finger mark from a known source was made. A volunteer’s forefinger was inked and introduced to a piece of paper. A ten print test card was also produced to be given to the analysts as comparison prints.
- This good quality clear mark was then super-imposed on a scanned image of a £50 note, positioned so the background obscured some detail. The mark was then manipulated to control the contrast and further obscure.
- A separate sample confirmed the fingermark was of poor quality and ambiguous.
- The clarity, size and quality was representative of prints they would normally receive.
groups in hall + player
Ppts asked to treat experiment as they would a typical day, they could come and go as they pleased, and talk among themselves as long as they did not discuss the finger mark or the experiment itself. No time limit was placed on the participants.They were assigned to one of two groups:
- The low-context group (35 participants) given an examination report referring to an allegation of forgery. chosen as it is considered a victimless crime and carries a relatively minor sentence.
- The high-context group (35 participants) was given an examination report referring to an allegation of murder. This was chosen because there is, inevitably, a victim and it carries the most severe sentence.
key info
The experts were then asked to consider whether the mark was
- An identification (a match)
- not an identification (not a match)
- insufficient—not enough detail to undertake a comparison,
- insufficient detail to establish identity, some detail in agreement but not enough to individualise.
asked to elaborate on findings by providing observations and opinions. also asked whether they had referred to the crime scene report and if they had, had it affected them.
methodof hall + player
Experiment – (although designed to be as naturalistic as possible as it took place in work time, in a typical fingerprint examination room, elements of control were used including analysts could not seek advice from each other.
IV of hall + player
whether the participant was allocated to the low-context or the high context group
DV of hall + player
Whether the participant considered the finger mark was;
- identification – a match,
- not an identification – not a match
- insufficient – not enough detail to undertake a comparison,
- insufficient detail to establish identity, some detail in agreement but not enough to individualise;
Whether the participant read the crime scene examination report prior to examining the fingerprint. Whether the participant would be confident to present the fingerprint as evidence at court.
