Psychology can be applied to help catch criminals through the criminal profiling process. A perpetrator does not leave behind just physical evidence at the scene when he or she commits a crime. They also leave behind clues about their behavior and personality. Profiling was originally introduced to investigate violent serial killers where catching the perpetrator is a matter of great urgency.
The forensic psychologist, or specially trained officer, builds a criminal profile from crime scene evidence and autopsy data. The psychologist seeks to find out how the killer gained access to the victim, what was the killer's attraction to the victim, what did the assailant do to the victim, and whether the killer then tried to cover his or her tracks. Most important, the profiler wants to know what motives and fantasies drove the killer to the crime. The profile helps narrow down the search for suspects and also guides the interrogation process. Knowing what kind of person the investigators are dealing with helps officers better formulate their questions.
The profiler will be also interested in the suspect's modus operandi (MO), which describes the tools and strategies used to carry out the crime. This reveals aspects of the suspect's behavior, which in turn reflects upon the suspect's personality.
Forensic psychology has revealed three main types of offender. The organized offender plans the crime, sometimes meticulously, bringing tools and taking them away again. This type of offender will take care not to leave evidence behind and will also hide or dispose of the body. The organized offender is usually of average to high intelligence with a stable lifestyle, tending to be married and employed. The disorganized offender often leaves a mess behind. They don't plan or bring tools; instead, they use whatever they find at the scene to attack the victim. This type of offender generally lives alone or with a relative, may be unemployed and have a history of mental illness. The attacks by this type of offender are often accompanied by considerable violence. The third category is the mixed offender, who shows some characteristics of the first two types. While the approach may be carefully planned, the assault itself may be frenzied, showing a person losing control over deep-seated urges and fantasies.
Another important aspect of criminal profiling is looking at the suspect's signature, which is a feature of the crime unique to that individual. It bears no relation to how the crime is actually committed but is very revealing about personality and motive. Examples of signatures include torture and mutilation, having sexual intercourse with the corpse, using excessive violence, or posing the victim after death in a particular way. Sometimes, as part of their signature, killers take away a trophy or souvenir that they may use to relive the crime later on. In the mind of the offender, a trophy is taken as a symbol of accomplishment, while the souvenir is an object taken to remind him of the event. Such items are often of little value in themselves, but can be very revealing about the psychology of the serial killer.
Research on the psychology of serial killers has revealed further trends. Most are male and in their 20s or 30s. Most murders of this kind do not cross racial lines; whites tend to murder whites and blacks murder blacks, etc. Most serial killers begin by hunting down victims close to home but, as their confidence grows, they may move further afield. Those with social skills, like Ted Bundy, may be able to trick their victims, while true loners tend to attack by surprise.
It can also be useful to profile the victim, to gain a full psychological picture of the crime. An understanding of the victim's lifestyle, habits, and behaviors may explain more about the suspect and why he chose this particular person to attack. Some victims are clearly at high risk of attack, if they meet many strangers, go out at night, and maybe if they make themselves vulnerable through drug or alcohol use or promiscuity. At the other end of the spectrum are low risk victims who stay close to home, do not venture out routinely at night, and have a steady routine job. Many people fall between these two categories. Whatever the type of victim, there is something about them that fulfils a serial killer's fantasies and then they are at great risk if they find themselves in the wrong place at the wrong time.
Criminal profiling was used to good effect to catch Carmine Calabro, who killed a young schoolteacher in 1979 with a pen and umbrella after raping her. Her mutilated body was placed in the shape of the Chai, which is the Jewish symbol of good luck. She was wearing a Chai pendant, which the killer seemed to have taken as a souvenir. This pointed to a disorganized killer driven by his own sexual fantasies. His profile would possibly be a person of low intelligence, with feelings of sexually inadequacy and a history of mental illness. This led the police to Calabro, an unmarried, unemployed 30-year-old whose father lived in the same apartment block as the victim. Calabro was undergoing psychiatric treatment at the time of the crime. Bites found on the body of the victim matched his dental anatomy and were instrumental in his conviction.
see also Psychological profile.