Profilers examine cases, mostly through crime-scene photographs, witness statements and evidence reports. They look for unique details that indicate the perpetrator's background, degree of experience and motivation. Based on his or her observations, the profiler develops a psychological profile of the perpetrator. The profile suggests how old the suspect might be, his or her past habits, lifestyle and even employment status. The profiler also tries to determine the gender, race, size, marital status and level of adjustment of the perpetrator — and often, the perpetrator's next move.

From a murder scene, a profiler might even reach astoundingly specific — and accurate — conclusions, such as a finding that the perpetrator has a speech impediment, post-adolescent acne or sexual dysfunction, or is someone who is socially inadequate. Or he may find evidence within the crime scene that the perpetrator might have known, and therefore deliberately stalked, the victim, rather than murdered at random.

Initially a hit-or-miss technique, the reliability of criminal profiling has improved with each passing year. There's even a national computer database into which investigators can enter information about known offenders in order to connect similar crimes committed across state lines. By conducting a signature crime analysis of different acts, the profiler tries to determine if certain behaviors link them together. Is it possible that the actions in different crimes emanated from the same source? Armed with his or her conclusions, the profiler can recommend appropriate courses of investigation.
His work requires long, concentrated study of the deepest psychological characteristics of most violent criminals. Overcoming the resistance of traditionalists, they are slowly changing the way that criminal investigations are conducted — and deepening our understanding of the nature of such horrifying acts in our society.