Confirmation bias is that process wherein an investigator develops a theory of the crime and thereafter filters facts, information and evidence, retaining that which conforms to his theory and discarding that which does not. It may be thought of as an attitude which colors the investigator’s approach. While “attitude” may be difficult to prove, confirmation bias always results in a failure to perform due diligence, as the filtering process requires the investigator to disregard facts and evidence and leads which should have been considered. A defense argument of confirmation bias should begin with a determination of a failure of due diligence.