Biological 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.

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.

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.

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.

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.

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:

1. Individual satisfaction in helping catch criminals in high-profile cases

2. Positive emotions with match fingerprints and fear of making an error

3. 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.

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:

• If written reports alongside evidence would affect the expert's analysis and understanding of poor-quality fingerprint marks

• If the emotional context of the case affects the experts.

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:

1. Whether participants read the reports (low or high emotional context) before the analysis

2. Their identification of whether:

   1. Fingerprints matched the crime scene fingerprint

   2. If they didn't match

   3. If the detail was not enough to compare

   4. If the detail was too vague to identify the fingerprint holder

   5. 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.

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.

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.