Collection and processing of forensic evidence Flashcards
Topic 2- criminal psychology
How reliable is forensic evidence?
-Contamination
-Weather
-People disrupting the crime -scene
-Insects
-Temperature
The 3 different types of finger prints left a the scene of the crime
- latent
-patent
-plastic
Latent finger prints
The finger prints are left behind from the natural oils on the skin leaving behind a trace, this is not visible to the naked eye so it would need enhancing
Patent finger prints
This would be visible to teh naked eye from it being in an impression in a fluid
blood, grease , soap bars, paint
Plastic
This is a a finger print has been moldes into something like wax, soap, putty or mud
Locating finger prints
This is done by dusting a powder on the finger prints which would stick to the prints
Porous surfaces
This is surfaces that are permable to air and fluids, the finger prints would be collected with chemical methods.
Non-porous surfaces
This is non-preamble to air and fluids which finger prints can be collected with powder techniques
Glass, metal, plastic
Reliability of finger printing
-Everybody has unique fingerprints
-False positives 0.1%
-Bias in fingerprints from the case that they may be involved with the suspects background might influence the case
Technical problems of taking a print
-context of the crime
-pressure of the case
- human error
-lack of independent features
The main motives
-rewards- job satisfaction
-satisfaction of catching criminals
-Solving long running cases
-feeling associated with searching for and finding matches
-need for closure in a case
-Fear of making a mistake
When does conformation bias occur?
-analysts look for evidence that would validate their current belifes and not contradict them
-when they feel under pressure to find a match
-where there is a high emotional context to the crime
-when several points of similarity are found and then further non points of similarity are assumed
What are the bias in collection of evidence
-conformity effect
-over-confidence bias
-selective attention
-observer or expectancy bias
-need determination perception
Conformity effects
If a fingerprint analysis is asked to validate the work of a peer or superior they may consciously agree with the decision being made
Over-confidence bias
Experts believe that they are always right, the more experienced the more they ignore the possible bias
Selective attention
Prior expectations can lead to the filtering out of ambiguous elements in an unclear prints where a close call has too be made
Observer or expectancy bias
The experts have pre-conceived ideas about the outcome of the case, this can come from know from knowledge of other cases.
Need determine perception
There is a strong desire to solve a crime
Case study- Madrid bomber
Te latent mark as identified incorrectly as Brandon Mayfield as he was on the FBI database already. The highly emotional context of this terrorist attack was thought to be the motivating factor for misidentification.
Aim-
hall and player- will the introduction of an emotional context effect fingerprint analysis and decision making?
-does the written report of a crime, as routinely supplied with fingerprints evidenced, affect a fingerprint expert’s identification of a poor quality print?
-are fingerprints experts emotionally affected by the circumstances of a case?
method/design-
hall and player- will the introduction of an emotional context effect fingerprint analysis and decision making?
-a laboratory experiment
-independent measures design
IV- low emotional context or high emotional context
DV- if the analyst reported feelings affected by the context
-judgments about the print (match/no match/insufficient detail/some detailed agreement not not enough to individualise)
sample-
hall and player- will the introduction of an emotional context effect fingerprint analysis and decision making?
-70 volunteer fingerprint experts
-working =for the metropolitan police
3 months to 30 years worth of experience- mean of 11 years
-58 were actively dealing with many different crimes
materials-
hall and player- will the introduction of an emotional context effect fingerprint analysis and decision making?
-fingerprint from a known source was used
- print scanned by computer and superimposed on the corner of a £50 note with the detail of the note obscuring the ridge detail
-14 prints were made a compared
-a sample of fingerprints confirmed that the print was ambiguous
each p was given:
-one of the 14 finger marks
-the suspects fingerprint on the 10 mark form
- a crime scene report
-a sheet of paper advising participants of the context and the information that the print was the right forefinger
procedure-
hall and player- will the introduction of an emotional context effect fingerprint analysis and decision making?
-p’s took part in their study as a part of their normal working day
-they were told act as they would in normal day
-they were told not to discuss this with any other people around them
-the p’s were ether given a high or low emotional case the the p’s would fill out a demographic sheet
-they were then ask to dicide wether the print was:
match
no match
insufficient detail
some detailed agreement not not enough to individualise
they were also asked to elaborate their observations and give details about their decisions
result
hall and player- will the introduction of an emotional context effect fingerprint analysis and decision making?
57 out of the 70 read the crime scene examination report before examining the prints
aim1:
-52% of the 30 who had red the high emotional context scenario felt effected by the information in the report
-only 6% felt affected in the low emotional context
-this indicated a relationship between the type of context and perceived effect on the experts
aim 2:
-the final decision made by the experts are very similar for the two emotional contexts and no significant difference was found
-when asked if they would be confident to present their findings in court slightly more confident in the low emotional context but it was not significant
conclusions
-emotional context does effect experts feelings but does not affect their overall analysis and judgement
-in comparison to the finding by Dror, experienced fingerprints expert are better at doing analysis in a detached manner than non-experts
evaluate
-population validity- this is experts
-ecological validity- high in ecological validity, not a real case, demand Characteristics
-usefulness- research raise awareness of errors and cognitive bias, this can be built into training forensic scientific to improve outcomes
strategies- combating context effects
- unaware towards the case information
- examine case information if necessary
strategies- ACE-V method
A- analysis- analysed and examined for details
C- comparison- taken from suspect and examine the similarities and differences
E- evaluation- side by sides and features and evaluated
V- verification- positive verifications buy a second expert
Exam questions
using research by hall and layer (2008) explain how motivating factors and bias could effect the collection and processing of forensic evidence (10 marks)
