Snowflakes are truly unique in their shapes. You may also have heard that fingerprints are unique in humans. Fingerprints are used as biological evidence in crime scene investigations. Society has developed many different systems based on the uniqueness of fingerprints and uses them as a tool of identification; however, issues arise when the reliability of the claim of uniqueness in fingerprints is not as scientifically robust as once thought.
- We are going to explore the use of biological evidence in criminal investigations.
- We will delve into the history and significance of fingerprint use in biological evidence. Then, we will discuss the famous cases of biological evidence used in crime investigations, thoroughly covering Brandon Mayfield.
- Here, we will highlight the importance of biological evidence before exploring biological evidence in forensic examples.
- We will also cover Hall and Player (2008) to illustrate our points before discussing other biological evidence examples.
- Finally, we will discuss ways to reduce bias in collecting and processing evidence.
Biological Evidence In Crime: The Fingerprint
The importance of biological evidence in crime means that it is vital the examples of biological evidence used are valid and reliable. Although the ridges of fingerprints are unique, the general shape of a fingerprint can be very similar. When used as biological evidence in crime scene investigations, fingerprint details are often lost. So can we confidently base judicial decisions on information that is not as accurate as it could be?
Fig. 1 - Fingerprints are unique, although details can be lost in investigations.
A fingerprint is classified and caused by the tiny ridges on the fingertips that evolved (supposedly) to help us grip things. They form when we are babies in the womb and stay the same throughout our lives. This consistency is why identification systems use fingerprints, including at crime scenes.
When used as evidence, one of the first things examiners analysing fingerprints from a crime scene need to establish is how many similarities exist between the fingerprint at the crime scene and the suspect's fingerprint.
Comparing similarities and differences allows them to identify if they are the same. Comparisons require high-visual accuracy, and other experts in different fields of study and research demonstrate how said experts develop particular efficiencies to excel in their analysis techniques.
Haller and Radue (2005) found that expert radiologists were more effective at interpreting images than novice radiologists when analysing manipulated or original images whilst undergoing functional MRI scans.
They found that experienced radiologists had higher neuronal activation in the bilateral middle and inferior temporal gyrus, bilateral medial and middle frontal gyrus, and left superior and inferior frontal gyrus. It was suggested this was due to high-visual efficiency resulting from appropriate and efficient schemata modification. Essentially, experience in the field allowed them to develop and hone their skills.
However, the image analysis required in radiology and fingerprint analysis is subject to human error.
Although expert fingerprint analysis requires extensive training, Risinger et al. (2002) identified that pressure can influence an expert's analysis of fingerprints presented to them from a crime scene.
In 1993, a supreme court case stated that scientific evidence used in court must be reliable and relevant. Not much research into the reliability of fingerprint evidence exists that questions whether we should use fingerprints in the courtroom.
Importance of Biological Evidence: The Case of Brandon Mayfield
Brandon Mayfield was arrested in May 2004 by the FBI due to the presence of a fingerprint found at the scene of a terrorist attack. The attack occurred on 11 March 2004. The Spanish National Police (SNP) found a fingerprint on a bag containing detonators in Madrid, Spain, and they asked the FBI to help identify potential suspects. A series of events began to occur.
Fig. 2 - Brandon Mayfield is a famous case in the use of biological evidence.
After running a computerised search on millions of other fingerprints stored by their database, the Integrated Automated Fingerprint Identification System (IAFIS), the FBI identified Mayfield. The search identified 20 possible suspects, and the FBI relied on human examination to compare the fingerprint at the crime scene with the potential suspects.
The expert in question stated it was Mayfield, which was corroborated by a second expert and reviewed by the Unit Chief, who acted as the third person in confirming Mayfield as a suspect based on the fingerprint.
The FBI investigated Mayfield quite heavily whilst the SNP investigated the fingerprint. On 13 April, they reported a negative result when comparing Mayfield to the fingerprint on the bag.
These results were concerning to the FBI, but what prompted an arrest was the media catching wind of a potential American terrorist involved in the attack in Madrid. The FBI arrested Mayfield on 6 May, fearing he would be alerted to their investigation and try to run.
Mayfield denied involvement and stated he did not know how they found his fingerprint on the bag. On 17 May, a court-appointed, independent expert reviewed the fingerprint and the FBI’s claims, concluding that the FBI was correct on 19 May.
The SNP then stated that they had found the actual suspect, Ouhnane Daoud, on the same day with identification on their fingerprint analysis. Mayfield was released on 20 May, and the FBI withdrew their statements on Mayfield on 24 May.
The International Panel of fingerprint experts investigated the situation over two days with the FBI to find out where things went wrong in this process, despite the FBI claiming the misidentification was due to poor image quality of the fingerprint, amongst other excuses.
They found the misidentification was essentially due to a domino effect. The first expert did not complete their analysis before using the FBI search database (IAFIS), there was overconfidence in the IAFIS, and there was pressure associated with the case.
Mayfield complained, filing a civil action in October 2004. Mayfield had an expired passport, had not left the continent in over ten years, and had also been at home on the day of the attack, as confirmed by family members.
Yet the FBI stated they were certain the fingerprint belonged to Mayfield. Fingerprint use was scrutinised, especially concerning how human error can impact results. Can biological evidence such as fingerprints be used as evidence in court?
Motivation and the Fingerprint: Biological Collection and Processing of Evidence
Experts in the department of fingerprint analysis have suggested multiple reasons for what influences their behaviours. Motivational factors are not only present in fingerprint experts. They affect human behaviours in all areas of life, so it stands to reason that these factors affect how a person performs in their career.
Charlton et al. (2010) found, using thematic analysis, that fingerprint experts refer to the following motivational and emotional factors:
Individual satisfaction in helping catch criminals in high-profile cases
Positive emotions with match fingerprints and fear of making an error
Cognitive closure in decision-making (the end goal)
Bias in the Courtroom: Biological Collection and Processing of Evidence
The situation with Brandon Mayfield came about due to human error, and psychologists conducted several studies to see how far human error can affect cases in the courtroom. Dror et al. (2005) investigated the effect of emotions on top-down processing in fingerprint analysis.
Top-down processing first involves operating with contextual information and working down to the raw data to form decisions.
In this study, 27 participants made 2,482 judgements on if a set of fingerprints matched each other. ¼ of these trials acted as a control. They manipulated the other trials in various ways, including emotional background stories given alongside the fingerprints, disturbing photographs, and subliminal messages.
They found that participants were affected by these manipulations and were more likely to match the fingerprints. The manipulations were influenced by how ambiguous the fingerprints were, however. The more ambiguous, the less the manipulations affected the judgements.
They concluded that top-down manipulations act as gap fillers and can affect judgment but cannot wholly dismiss bottom-up issues. Dror then went on to suggest these human errors were due to how cognitive biases influence the top-down process, namely:
Confirmation bias
Expectancy bias
Selective attention
Over-confidence
Biological Evidence In Forensic Examples: Hall and Player 2008
Hall and Player (2008) aimed to see if experts in the field of discerning fingerprints would be affected by the emotional components of a case, as experts were tasked with identifying the differences and similarities in the ridges in fingerprint marks. As judgement relies on human observation and expertise, results are subjective and can be affected by human error.
Specifically, Hall and Player (2008) aimed to identify the following:
It was a field experiment with an independent measures design using a random allocation of participants. The manipulations included low emotional context (victimless crimes) and high emotional context (murder).
The study included a sample of 70 fingerprint experts with an average of 11 years of experience actively engaging in fingerprint analysis work. The independent variable was the allocation of low or high-emotional context groups. The dependent variables were:
Whether participants read the reports (low or high emotional context) before the analysis
Their identification of whether:
Fingerprints matched the crime scene fingerprint
If they didn't match
If the detail was not enough to compare
If the detail was too vague to identify the fingerprint holder
Whether the experts would be confident enough to present their analysis in court
A fingerprint was obtained from a volunteer and, using ink, was placed onto paper and then transferred to a £50 note. The ridges were hard to discern due to the £50 note affecting the quality of the fingerprint. Participants had to compare this with ten other fingerprints and information telling them what finger it was from (right forefinger).
They were able to use some tools to help them see the details of the fingerprints (Russel comparator and magnifying glass). They had to indicate solely if the fingerprints matched or not.
The results indicate that more than half read the crime scene report before examining prints, 57 out of 70 in total, and 30 contained high-contextual information we mentioned above.
- 52% of the high-context experts stated they were affected by the information
- 6% of the low-context experts stated they were affected by the information
However, despite this significant difference, there were no significant differences between the final decisions. Similarly, both contexts showed no significant differences in if the experts would present their findings in a courtroom.
Hall and Player (2008) concluded that emotional context appears to have little influence on an expert’s final decision in fingerprint analysis, and they can remain emotionally neutral in this process.
The study had issues with ecological validity, as this is not how experts typically receive and analyse fingerprints. It may also suffer from demand characteristics. Hall and Player (2008) said that more research into the length of service and the seriousness of the crime is needed, as this was only a single study on the topic.
Examples of biological evidence
Although we have discussed fingerprint analysis at length for your exam, there are other examples of biological evidence in crimes, most if not all, providing clues about possible suspects through DNA (deoxyribonucleic acid). These include:
Blood samples
Hair samples
Skin cells
Saliva samples
Strategies For Reducing Bias in Collecting and Processing Evidence
Forensic teams can reduce issues with bias in the collection and processing of evidence in several different ways.
Reducing the emotional stimuli given alongside the evidence
Removing details irrelevant to the case, as these are not necessary for fingerprint matching (such as just providing the fingerprint)
Encourage other experts to weigh in on matters to provide blind verification of the fingerprint match.
For instance, expert one provides a result, and then expert two conducts their analysis without knowing anything expert one said to provide their results, too.
Biological Evidence in Crime - Key Takeaways
- Biological collection and processing of evidence in crimes include fingerprint analysis.
- Fingerprint analysis involves examining ridge details in your fingerprints, where experts determine similarities and differences to other fingerprints.
- The reliability and validity of fingerprint use as evidence have been questioned, especially concerning issues with human error.
- The case of Brandon Mayfield highlighted issues with the use of fingerprints. Hall and Player (2008) concluded that emotional context appears to have little influence on an expert’s final decision in fingerprint analysis, and they can remain emotionally neutral in this process.
- Dror et al. (2005) suggested cognitive biases were to blame: confirmation bias, expectancy bias, selective attention, and over-confidence.
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