Confirmation Bias in Investigations


In a 2012 paper titled “The Psychology of Bias: Understanding and Eliminating Bias in Investigations (Oppenheimer, B.A. (2012)), Amy Oppenheimer defines confirmation bias as, “. . .

the tendency to bolster a hypothesis by seeking consistent evidence while minimizing inconsistent evidence. It involves unconscious information processing rather than deliberate case building. Once a hypothesis is formed, people tend to search for information that supports it. For investigators, this means that by focusing primarily on a favored hypotheses, investigators may fail to generate alternatives and thus do not see the relevance of information supporting another explanation.”


Most of us have seen the scenario on television and the movies where the seasoned Detective looks at the crime scene and states confidently, “Here’s what happened.” Although this plays well in fiction, it is a dangerous mindset in real life investigations. People, including investigators, tend to go with things that agree with us and our existing beliefs. And, since nobody likes to be wrong, it is easy for investigators to agree with people who agree with them, focus on the evidence that supports a pre-formed theory (or suspect), and possibly apply less weight to evidence that counters that pre-formed theory.


In a July 17, 2014 article titled “Dealing With Confirmation Bias” for POLICE Magazine, Amaury Murgado recounts an excellent example of how confirmation bias can adversely affect the search for truth. An attorney from Oregon named Brandon Mayfield was erroneously linked by the FBI to the 2004 Madrid train bombings when two latent fingerprints were found by Spanish authorities on a bag containing detonating devices. The FBI identified approximately 20 possible matches for one of the fingerprints, one of whom was Mayfield whose prints were in the FBI system due to Mayfield's military service and from an arrest approximately 20 years earlier where charges were dropped. Although Mayfield's print was not an identical match to the print left on the bag of detonators, the FBI rationalized away the differences. According to a report by the Department of Justice's Office of the Inspector General (which can be found here), certain details of the attorney's life convinced the FBI that Mayfield was involved such as Mayfield’s conversion to Islam and work he performed for the Modest Means Program of the Oregon State Bar, which matched attorneys who are willing to work at reduced rates for low-income clients, where he represented one of the Portland Seven (a group of men who tried to travel to Afghanistan to fight for Al Qaeda and the Taliban against U.S. and coalition forces) in a child custody case. The FBI arrested Mayfield as a material witness in connection with the Madrid attacks. When the FBI finally sent Mayfield's fingerprints to Spanish authorities, they informed the FBI they had other suspects in the case, not linked to anyone in the USA, and that their opinion was that Mayfield’s fingerprints did not match the evidence in the case. This seemed to have been ignored by the FBI. Mayfield was eventually released and the FBI apologized. As one can imagine, litigation and a hefty settlement followed.


This case is an example of what happens when investigators cling to information that supports a pre-existing theory while at the same time ignoring other information that runs contrary, no matter how valid or factual that information may be.


It is easy to see where this form of bias can create problems in what should be an objective investigation. The investigator forms an opinion and a theory of the case, then works to prove it right instead of focusing on objectively gathering facts. This is true in any investigation, not lust law enforcement. It can also happen in internal corporate investigations, the type of case in which we at Overwatch Risk Solutions are very experienced. Many times, we are told from the outset by a reporting party or other company official, "I know she did it" or “it had to be him”. Our personal favorite is, “he has always been a problem employee, I’d focus on him”. But when the person is asked how he knew it was that individual and asked to provide what evidence he had to support his theory, often times the answer is something like, "Because I just know; my gut tells me."


So how does the professional investigator avoid confirmation bias from tainting the investigation? First and foremost, avoid reaching conclusions until enough information has been collected and analyzed. Then, let the evidence point the way.


Investigators must make the conscious effort to avoid tunnel vision and accept all information that comes their way. Information should never be excluded until all the information is in and is put in context. There have been numerous cases where certain information was automatically excluded from consideration because it appeared not to be related to anything at the time. Then, as more information is gathered, the previous information that was so quickly dismissed comes into focus. It is much like putting a puzzle together. Sometimes, you have puzzle pieces that do not seem to fit anywhere but, as you continue to build the puzzle, those seemingly useless pieces fall into place to complete the picture. For example, in an embezzlement investigation we were conducting, we came across a check to a seemingly random company for specified logistic services. The payment was buried deep in accounts payable records and, at first look, seemed to be totally unconnected from the case we were pursuing. As we continued the investigation and gathered more information, it became clear that the payment we thought was an outlier was actually one of numerous payments, in different company names, all deposited one bank account held by an individual that, up to that point, was unknown to us. In the end, the individual that the company felt was the prime suspect was just another unwitting victim of the fraud scheme.


As an investigator, continually test yourself. Review what you think you know and then ask yourself, “How do I know this? Is it based upon facts or opinion?” Sometimes our opinions and theories work their way in to our minds and it is useful to continually fact check ourselves.


It takes work to ensure an investigation remains objective and to remain impartial. However, in order to get to the truth, it is imperative that investigators stick to, to coin a phrase, “just the facts” and allow the evidence to point the way.

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