In 1979, Montana's insanity defense was replaced with the more
restrictive mens rea defense, a change that has been described as an
example of "abolition" of the insanity defense. The authors identified
cases in which mental health was an issue in seven Montana counties for 3
years before and 3 years after the 1979 reform. They found that acquittals
based on the insanity plea markedly declined, but that dismissals based on
incompetence to stand trial increased substantially following the reform.
They conclude that dismissal based on incompetence to stand trial became a
substitute for acquittal based on the insanity plea under mens rea.