Noun
(criminal law) a plea in which the defendant claims innocence due to mental incompetence at the time
Source: WordNetIs not this insanity plea becoming rather common? Is it not so common that the reader confidently expects to see it offered in every criminal case that comes before the courts? [...] Really, what we want now, is not laws against crime, but a law against insanity. Mark Twain
We have an insanity plea that would have saved Cain. Mark Twain