Collection and Processing of Forensic Evidence (2)

Question 1

What are the pros and cons of forensic evidence?

Answer 1

• useful in comparison to witness testimony as more objective and less vulnerable to bias
• however can still be subject to bias as human expert is vital in making a final judgement
• e.g. Brandon Mayfield wrongfully detained in connection with 2004 Madrid train bombings on the basis of a faulty fingerprint match
• Hampikan et al. (2011) reviewed number of wrongful convictions and found forensic evidence was involved in a variety of ways (e.g. 38% contained incorrect blood analysis, 22% contained incorrect hair comparisons)

Question 2

What is confirmation bias?

Answer 2

• when experts focus more on evidence that confirms their beliefs and ignores evidence that contradicts them (either knowingly or unknowingly)
• most evident in the comparison of the latent fingerprint (from the crime scene) to the comparison print (given when suspect arrested)
• more marked when the quality of the fingerprint is poor (as decisions are more subjective)

Question 3

What factors can affect this bias?

Answer 3

• in a study of non-experts, Dror et al. (2005) found that in highly emotional contexts the likelihood of an ambiguous pair of fingerprints being “matched” is significantly higher
• indicates that highly emotional contexts are likely to result in type I errors
• might heighten emotional context of crime: type of crime, nature of victim/suspect and the type of photos included in the case file
• even experienced analysts can have issues as a result of “circular reasoning” –> once similarities are found, others are “found” to support them

Question 4

What was the aim of Hall and Player’s study?

Answer 4

• the protocol used by the Met Police involves providing fingerprint examiner with a copy of the crime scene report, which details the nature of the crime but doesn’t provide any imagery
• Hall and Player thought it was important to ascertain if these practices introduce an emotional bias by investigating:

1- does the written report of a crime, as routinely supplied with the fingerprint evidence, affect a fingerprint expert’s interpretation of a poor quality mark?

2- are the fingerprint experts emotionally affected by the circumstances of the case?

Question 5

What method did Hall and Player use?

Answer 5

• lab experiment (although designed to be as naturalistic as possible, taking place during working hours in a typical fingerprint examination room)
• control element: analysts could not seek advice from each other
• IV: whether the participant was allocated to the low-context or the high-context group
• DVs:
  1- whether the participant read the crime scene examination report prior to examining the fingerprint
  2- whether the participant considered the finger mark as a) an identification, b) not an identification or c) insufficient

Question 6

What sample did Hall and Player use?

Answer 6

• participants responded to a request for volunteers to take part in an experiment
• 70 fingerprint experts working for the Met Police Fingerprint Bureau took part
• length of experience as experts ranged from <3 months to 30yrs (mean 11yrs)

Question 7

What was the procedure of Hall and Player’s experiment?

Answer 7

• in order to validate the decisions of experts, a finger impression from a known source was used
• ten print test card also introduced to be given to the analysts as comparison prints
• good quality clear mark scanned and super-imposed on a scanned image of a £50 note, positioned so the note background obscured some detail
• mark then manipulated to control contrast and further obscure
• clarity and quality was representative of those received irl
• participants asked to treat the experiment like a typical day: could come and go as they pleased as long as they didn’t discuss the prints
• no time limit

Question 8

What was the difference between the high context group and the low context group?

Answer 8

• low context: given examination report referring to allegation of forgery
• chosen because victimless and carries a relatively minor sentence
• suspect tried to pay with a forged £50 note then left the scene
• high context: examination report referring to allegation of murder
• chosen because there’s a victim and carries a more severe sentence
• suspect fired two shots before decamping

Question 9

What were the results of Hall and Player’s study?

Answer 9

• 57/70 participants read crime scene examination report prior to examining prints: more of these in high context group
• 52% of those who read high context scenario felt they were affected by info given on report, compared to only 6% in low contact scenario
• this indicates a relationship between the type of context and the perceived effect on the experts

Question 10

What was the conclusion of Hall and Player’s experiment?

Answer 10

• emotional context does affect analysis of the finger print but this has no effect on the outcome
• seems that details of the crime are surplus to requirement, so it may be best not to provide them, so as to keep the process as objective as possible
• important to note that such analysis only forms part of the final info presented in court

Question 11

What strategies can be used to reduce bias in the collection and processing of forensic evidence?

Answer 11

1. Educating detectives, judges and juries about strengths and weaknesses of forensic science
2. Training forensic examiners to minimise bias
3. Introducing appropriate protocols
   - e.g. limiting access to case info that is not necessary to reach a decision
   - verifier: second person who analyses without knowledge of decision made by first
4. Providing analysts with a “line up”