Identifying patterns among their research subjects, Douglas’ team believed that common traits, ages, habits, and other demographic details could be used to construct accurate profiles of criminals simply from the evidence at hand. Everything from the location and appearance of a crime scene to the arrangement of a victim’s body was relevant. They identified key characteristics of certain criminals, ranging from a personality afflicted with feelings of inadequacy to the tendency by some to indulge in fantasies.

Immersion in these cases has affected Douglas not only mentally, but physically as well. In 1983, Douglas nearly died from viral encephalitis while working in Seattle, Washington on “The Green River Murder” case. Doctors later attributed his illness as a result of the heavy workload he carried and dealing on a daily basis with crimes of violence. Although diagnosed with “post-traumatic stress disorder” Douglas continued to oversee 1,000 violent crime cases annually that both he and the 12 FBI profilers, who he affectionately referred to as “The Dirty Dozen,” would work tirelessly on.