Profiling a killer

The latest in my ‘Learn Something New Every Day’ series – taken from The Great Courses’ Trails of Evidence: How Forensic Science Works (Lecture 27 – Profiling)

Offenders get broken down into two main behavioural groups: organised/disorganised

  • Organised offenders are prepared and usually plan their attacks meticulously.
  • Disorganised killers are impulsive: they don’t plan their attacks and they’ll use found objects (knives, bottles, blunt objects) and will typically leave a lot more evidence behind. Can ‘mature’ into an organised criminal if not caught early and so crime fighters are very eager to catch them before they become proficient.

There are three reasons a perpetrator might take something from a crime scene:

  1. Item has evidentiary value (eg: they think it might have their prints or blood on it)
  2. The item has monetary value (theft)
  3. The item has psychological value (trophy) for a perpetrator who wants to remember his accomplishment/victory/actions

Modus Operandi (MO) is the usual method of committing a particular crime for organised criminals. It’s a conscious process. You’d think criminals would be smart enough now to know not to use the same MO, but they work for criminals because:

  1. enables them to successfully complete their criminal act (practice makes perfect)
  2. prevents identification (if they’ve done it before they know how to get away with it)
  3. eases their escape from crime scene (they’ve worked the kinks out of the escape plan)

Criminal signature is different to MO and most signatures are unconscious. Signatures are based on inner/psychological drive from a criminal’s fantasy. Often signature is a small element within the MO (like, say, ripping the left earring out of a victim’s ear) which can help investigators to identify evolving criminals/MOs.  MO’s change, signatures rarely do.