When the Washington, D.C.-area snipers were still at large, investigators told the public that the assailant was probably driving a white box truck or van. All over the region, police and drivers cast a wary eye at these vehicles, while the snipers’ actual vehicle, a dark blue Chevrolet Caprice, went disregarded. This is an example of a “cognitive bias”; it delayed the capture of the snipers and often leads to false arrests or wrong accusations. Other such biases include spurious cause and effect. In one series of rapes on the south side of a city, for example, police hypothesized that the offender stalked his victims from a local superstore, where all of his victims had shopped. It turned out that almost everyone from the south side shopped there, and that there was no connection between the store and the crimes.
In an article in the FBI Law Enforcement Bulletin, D. Kim Rossmo, a former detective and a criminal justice professor of criminal justice at Texas State University in San Marcos, discusses various cognitive biases that lead investigators astray and offers strategies to combat them.