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Biological Evidence

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Biological Evidence

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. 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, the detail of fingerprints is often lost. So can we confidently base judicial decisions on information that is not as accurate as it could be?

Biological Evidence in Crime, eight different types of fingerprint patterns, StudySmarterFingerprints are unique in their ridges but similar in their swirls, freepik.com/pch.vector

Biological evidence in crime: the fingerprint

One primary tool used in biological evidence at crime scenes is the fingerprint.

A fingerprint is classified and caused by the tiny ridges present on the fingertips that evolved (supposedly) to help us grip things. They form when we’re a baby 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, analysis of images required in both radiology and fingerprint analysis is subject to human error.

Although experts in fingerprint analysis require 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.

Biological Evidence in Crime, timeline of Brandon Mayfield and FBI fingerprint misidentification, StudySmarterBrandon Mayfield was incorrectly identified due to fingerprint analysis by the FBI, Tyler Smith, StudySmarter Originals

  1. 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.

  2. 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.

  3. The FBI investigated Mayfield quite heavily, whilst the SNP did their investigation on 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.

  4. Mayfield denied involvement and stated he did not know how they found 'his' fingerprint on the bag.

  5. On 17 May, a court-appointed, independent expert reviewed the fingerprint and the FBI’s claims, concluding that the FBI were correct on 19 May.

  6. 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.

  7. 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.

  8. 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.

  9. 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 came under scrutiny, 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 involves first 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 completely 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:

  • 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 would affect the experts.

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:

  • Overall, 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 overall

  • 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 normally 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 how serious the crime is is needed, as this was only a singular 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

Strategies forensic teams can use to reduce issues with bias in the collection and processing of evidence include:

  • 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 cases, 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. The FBI had three separate experts and a unit chief confirm his fingerprint as the one present at the crime, despite Mayfield having an expired passport. Mayfield also hadn’t left the country in ten years. The Spanish National Police eventually found the real suspect.
  • Dror et al. (2005) suggested cognitive biases were to blame, namely confirmation bias, expectancy bias, selective attention, and over-confidence.
  • Hall and Player (2008) concluded 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. Strategies to avoid bias include blind verification, removing contextual information, and reducing emotional stimuli given to the experts.

Frequently Asked Questions about Biological Evidence

Five types of biological evidence in crime include:


  • Fingerprints
  • Blood samples
  • Hair samples
  • Skin cells
  • Saliva

Biological evidence includes any substance that contains a person's DNA. Biological materials that include a person's DNA can be blood samples, hair samples, saliva, bodily fluids, and skin cells, among other examples. Fingerprints also serve as biological evidence in crimes.

Biological evidence can directly identify a person's DNA to determine if they were at a crime scene and If they are a potential suspect. Biological evidence can also compare suspects to DNA found at a crime scene, for example, a fingerprint comparison or blood samples.

DNA is a form of biological evidence and can be extremely accurate depending on what form of DNA is used to identify potential suspects. It can point investigators down the correct path and lead them to suspects they would not normally have identified through psychological evidence alone.

DNA is collected carefully to avoid contamination issues. Investigators will often wear protective clothing to protect themselves and the samples and ensure DNA is not mixed with other potential sources. DNA is then kept in air-dry packages to avoid degradation issues. 

Final Biological Evidence Quiz

Question

What are five types of biological evidence used in crime scenes?

Show answer

Answer

Five types of biological evidence in crime include:


  • Fingerprints
  • Blood samples
  • Hair samples
  • Skin cells
  • Saliva

Show question

Question

What causes the unique details found in fingerprints?

Show answer

Answer

The ridges present determine fingerprint uniqueness, forming when you are a baby in the womb and staying the same throughout your life.

Show question

Question

How do experts analyse fingerprints from a crime scene?

Show answer

Answer

They establish how many similarities and differences exist between the fingerprint from the crime scene and the suspect's fingerprint. 

Show question

Question

What famous case highlighted the issues with the reliability and validity of fingerprint analysis in crime?

Show answer

Answer

Brandon Mayfield, in 2004. 

Show question

Question

The FBI had __ separate experts and a unit chief confirm Mayfield's fingerprint as the one present at the crime scene.

Show answer

Answer

3

Show question

Question

The Spanish National Police eventually identified the real suspect, different from the FBI's Brandon Mayfield - true or false?

Show answer

Answer

True

Show question

Question

Charlton et al. (2010) found, using thematic analysis, that fingerprint analysis experts are affected by what emotional and motivational factors?

Show answer

Answer

  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)

Show question

Question

Fingerprint analysis is subject to _______.

Show answer

Answer

Human error

Show question

Question

Dror et al. (2005) investigated top-down processing in fingerprint analysis. What did they find in their study?

Show answer

Answer

  • They found that participants were affected by manipulations (emotional background stories, disturbing images, subliminal messages) 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 completely dismiss bottom-up issues. 

Show question

Question

According to Dror which human errors were a result of which cognitive biases influencing the process? 

Show answer

Answer

  • Confirmation bias
  • Expectancy bias
  • Selective attention
  • Over-confidence

Show question

Question

What were the aims of Hall and Player (2008)?

Show answer

Answer

  • To identify if written reports alongside evidence would affect the fingerprint expert's analysis and understanding of poor quality fingerprint marks. 
  • To identify if the emotional context of the case would affect the experts.

Show question

Question

What did Hall and Player (2008) manipulate in their study?

Show answer

Answer

The manipulations included low emotional contexts (victimless crimes) and high emotional contexts (murder).  

Show question

Question

How many fingerprint experts were included in the Hall and Player (2008), and how many years of expertise did they have?

Show answer

Answer

The study included a sample of 70 fingerprint experts with an average of 11 years of experience actively engaging in fingerprint analysis work. 

Show question

Question

What was the fingerprint inked onto in the study by Hall and Player (2008)?

Show answer

Answer

A £50 note.

Show question

Question

What were the results of Hall and Player (2008)

Show answer

Answer

  • Overall, 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 overall
  • Similarly, both contexts showed no significant differences in if the experts would present their findings in a courtroom

Show question

Question

How can bias be reduced in the biological collection of evidence in crime?

Show answer

Answer

  • Reducing emotional stimuli given alongside evidence
  • Removing irrelevant details to the case/fingerprint matching process
  • Encourage other experts to weigh in on cases and use blind verification

Show question

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