Confirmation bias in suspect interviews
Richard had always wanted to be a police officer. He had achieved all of the grades that he needed at college and was accepted to train as a police officer. Richard passed all of his classes during training and eventually got to a point in in his training were he had to learn interview techniques. With his friend Samuel, Richard role-played interview techniques. Together they were told that they should familiarise themselves with the facts of the case before interviewing a suspect. When Richard was told to familiarise himself with the facts prior to interviewing he thought it odd because he knew that the interviewing officer would then suspect guilt or innocence. Despite his initial suspicions about the interviewing method like all of his colleagues he continued to interview in the way that he was trained.
The justice system is one of the most important systems a country can have, it keeps order and ensures that anyone who commits a crime is treated in the relevant way to that country. One of the main ways in which the justice system operates is through the use of law enforcement (i.e., police officers). Police officers get called to the scene of a crime, assess the scene, collect evidence and detain anyone that is suspected of the crime. We like to think that police officers always make the correct decisions, however like anyone else they are fallible.
One the most problematic cognitive biases (errors in decision-making) is the confirmation bias. The confirmation bias happens when an individual is required to make a decision but set about trying to prove a hypothesis that they already have. By making a decision based on what they already believe the individual is therefore at risk of making an incorrect decision.
One study that set out to investigate the confirmation bias in experienced police officers recruited 89 police officers. Charman and colleagues (2017) gave fictional criminal cases to participants and asked them to make a judgement about the guilt or innocence of the fictional suspect. Participants were then presented with ambiguous evidence in the form of either an alibi statement, handwriting sample, composite, or details of an informant (see Table 1) and asked to evaluate the ambiguous evidence. The results of this experiment found that the evaluation of the ambiguous evidence was related to the initial judgement of evidence in police officers: the stronger an officer’s initial belief in a suspect’s guilt the more incriminating they perceived the ambiguous evidence to be. The confirmation bias clearly had a strong effect in the evidence gained from interviews.
An extreme case of confirmation bias during suspect interviewing can be demonstrated by what is one of the most publicised criminal case in recent years, the November 2007 murder of Meredith Kercher in Perugia, Italy. On the second of November 2007, British exchange student Meredith Kercher was found dead by her roommate, American, Amanda Knox. Knox had no history of violent crime and lacked a motive. When the police took a statement from Knox they believed she was hiding something because she showed no sign of emotion and behaved immaturely. She stated that on the night of the murder she was with her Italian boyfriend Raffaele Sollecito. With the prejudgement of Knox’s guilt, the police interrogated her for four days in Italian, a language that she was not fluent in, and without a lawyer present. In the early hours (1:45 am) of the fourth day of interrogations Knox eventually broke down, started screaming and without the support of her family and friends confessed to the murder. Later, when left alone she retracted her confession in a written statement. Interestingly, the confession contained no new information and was in part factually incorrect on important details. Knox was then officially arrested with Sollecito and provided with a lawyer. Her lawyer had the confession ruled inadmissible in court. Nonetheless, in the investigation that followed set about a motion of hypothesis-confirming (i.e., try to confirm a prior belief of guilt) with the detectives determined to prove that Knox was guilty (Kassin et al., 2011). In due course, on the 5th of December 2009 a jury convicted Knox and Sollecito of murder. Knox was sentenced to 26 years in prison and Sollecito to 25 years in prison. Eventually, on the 3rd of October 2011 after being granted a new trial, both Knox and Sollecito were acquitted. A short time after the release of Knox and Sollecito the Italian appeals court released a 143-page opinion criticising the prosecution concluding that there was no credible evidence or motive to presume Knox’s guilt.
One of the possible influences that brings about the confirmation bias in police interviews are the guidelines from the United States Department of Justice (Eyewitness evidence: a guide for law enforcement. U.S. Department of Justice, Office of Justice Programmes). These guidelines state that an interviewer should review the case information prior to conducting an interview, of course, at first thought this seems like ‘common sense’. A study by Rivard and colleagues in 2015 investigated this and how to prevent confirmation bias errors in suspect interviews. The results of their study found that blind interviewers (those that do not know the details of the case prior to the interview) produced more correct judgements of guilt or innocence than those that knew the details prior to interviewing a suspect. Another benefit of using blind interviewers is that in this study they did not start the interview with a suggestive / leading question.
In the United States alone the Innocence Project (2015) estimates that more than 300 innocent people have been wrongfully accused and convicted of crimes that they did not commit because of investigator bias and eyewitness error. Although some section of our justice systems are aware of the confirmation bias, and train their staff in the knowledge of the confirmation bias, it is hard to avoid this entirely. We have seen one way of the ways in that we can use to avoid the confirmation bias in the study by Rivard et al (2015), although this method may cause other problems itself. The confirmation bias is not unique to suspect interviews since these types of errors in decision-making are a problem in many situations when decision needs to be made (e.g., medical, legal, sports etc). So like Richard going through his police training, if you are unsure about a decision you can simply get a second opinion or take a step back and think carefully.