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As one of the most commonly depicted characters in novels, films, and television shows, the police detective solves complex criminal investigations through deductive skills, high-tech forensics, specialized computer programs, hard work, and luck. In these fictional accounts, good wins, evil loses, and justice triumphs. But, in the real world, investigations do not always turn out that way. Sometimes, the case stays open, the criminal remains at large, and justice is denied.
Failures in the criminal investigative process can have serious consequences. Unsolved crimes, unsuccessful prosecutions, unpunished offenders, and wrongful convictions bring the criminal justice system into disrepute. In addition, with the cost of some major investigations climbing into the hundreds of thousands, even millions, of dollars, wasted efforts can prove extremely expensive.
Most investigators, however, are competent, dedicated professionals who want to solve their cases and arrest the right people. So, what causes a major crime investigation to fail or a criminal prosecution to focus on an innocent person? The answer lies primarily in the subtle hazards or traps that can make the process go awry. Some of the brightest scientists, judges, and detectives have fallen victim to these pitfalls. No one is immune. Researchers in the fields of cognitive psychology, forensic statistics, intelligence analysis, law, and the philosophy of science, however, have suggested some possible explanations, often grouping them into the three areas of cognitive biases, probability errors, and organizational traps. Like cascading failures in airplane crashes, an unsuccessful investigation often has more than one contributing cause.
To fully examine these pitfalls, the FBI Law Enforcement Bulletin presents this article in two parts. The first covers cognitive biases that can lead to criminal investigative failures and some strategies that can combat their occurrence.
COGNITIVE BIASES
Perception and Memory Limitations
People do not objectively survey their worlds. Rather, their experiences and expectations influence the decoding of sensory input (imperfect at best1). Individuals view the world through different lenses, a filtering process that creates mind-sets.2 Quick to form but resistant to change, mind-sets, while neither good nor bad, serve a purpose that under certain conditions can become problematic. Because perception is based on both awareness and understanding, humans often perceive what they expect to, thereby making premature conclusions dangerous. Communication becomes doubly subjective as it involves...