Research in neuroscience supports that our brains are "predictive machines" and that what we perceive is a result of not only our external world, but also our internal biases, beliefs and experiences. In addition, our brains tend to "explain away" anything that does not line up with our predictions or beliefs. So how does this impact investigative interviewing and criminal interrogation?
Imagine a detective entering into an interrogation with the belief that the suspect is guilty of the crime under investigation. Based on that belief the detective may then predict that the person will likely lie about their involvement in the crime. Therefore, anything the person says or does will be filtered through this lens by the detective's brain and look for things to support that prediction. This issue is compounded when the detective has misinformation about what deceptive behavior looks like, so if the person shifts in their chair or scratches the back of their neck they may conclude it is due to them lying.
If there is evidence or testimony from another source that comes to light which lends credibility to the suspect's account, that information may be overlooked or discounted, and may be explained away by the detective. For instance, testimony from a friend who states that the suspect was with them at the time of the incident and therefore could not be involved, may be viewed with suspicion and doubt, leading the detective to conclude that the two of them have conspired to line up their stories.
This is not only supported through psychology and cognitive science with the issue of confirmation bias, but also neuroscience which tracked the electrical activity within the human brain, so it is a psychological and biological issue as well. For more research on the predictive nature of the brain, click HERE.
The way I approach investigative interviews, and the way I teach it as well, is to start with the belief that the person will tell the truth, but also understand they anyone may lie. Use this neutral approach and probe their account fully and have them expand upon their story and the information they provided through proper questioning. Focus more on their account and the words they use, and don't try to interpret their behavior, but rather use it as a marker to probe with further questioning. By not entering the interview with a preconceived beliefs, but just having the focus on gathering as much information as possible from them, and by using an effective questioning strategy throughout the interview, it will help improve your ability to gather and evaluate the information more effectively and you will be less likely to be misled by the issued described above.