Pleading Insanity

Nearly there… only a few more lectures to go in this very interesting, very long course Trails of Evidence: How Forensic Science Works (Lecture 29: Forensic Psychology/Psychiatry)

Only 1 in 100 cases in the US includes an insanity plea and, of those, only 1 in 10 are found to be criminally insane. Given the 1 in 1000 rate of success, Hollywood and popular media seriously over-represent this legal defence.

  • ‘Not guilty by reason of insanity’ An 1843, British-born legal principle called the M’Naghten Rule says that “If the defendant did not or could not understand what he/she was doing or that it was wrong, at the time of the crime they are considered not guilty by reason of insanity.”   Someone found not guilty in this manner would not go to prison but would almost certainly go to some kind of psych institution where, with no criminal conviction recorded, they could be released after full assessment/treatment.  Or not.  The US has recently modified this age-old tenet to include someone who *did* know that what they were doing was wrong but couldn’t control their behaviour. The M’Naghten Rule was named for Daniel M’Naghten a psychotic individual who shot the British Prime Minister’s secretary (while aiming for the Prime Minister) after becoming convinced that the PM wanted to kill him. He was acquitted (on grounds of insanity) but the House of Lords formalised a new rule for insanity to help with such cases in the future.
  • ‘Guilty but mentally ill/insane’  After John Hinckley was found not-guilty (by reason of insanity) of shooting US President Ronald Regan, a further concept was added to US justice – ‘guilty but insane’. This provides for those who are clearly mentally ill but ensures they are convicted of their crime. Their incarceration may be a prison or a psych institution.
  • ‘Diminished capacity’ – defendant broke the law but due to impaired mental function should not be held liable for their crime.