Definition
The FBI Behavioural Science Unit (BSU) method is the original American approach to offender profiling, developed by John Douglas, Robert Ressler, and colleagues at Quantico in the late 1970s. It rests on a typology of serial offenders — most famously, the organised / disorganised distinction — derived from interviews with a small sample of incarcerated serial killers.
In the BSU framework, organised offenders plan crimes meticulously, leave little evidence, target strangers, and are socially competent; disorganised offenders act impulsively, leave evidence, know their victims, and are socially marginal. The crime scene is read for indicators of which type produced it, and a corresponding offender profile is generated.
Why it matters
Where it shows up
The BSU legacy is preserved in the FBI's National Center for the Analysis of Violent Crime and in many training programmes worldwide. The typology persists in popular culture even as it has been substantially superseded in research. It remains a useful teaching device for the history of profiling, less so as a current operational tool.