In 1982, American jurisprudence sustained a crushing setback from which it has yet to recover. The iconic date is June 21 of that year, when a jury in Washington, DC, found John W. Hinckley Jr., the profoundly disturbed young man who shot President Ronald Reagan and three other men, not guilty by virtue of insanity. The verdict set off a firestorm of outrage that crossed the geographical and political divide; one day after the verdict was announced, an ABC News poll heard 83 percent of respondents proclaim that "justice was not done."
Juror Lawrence Coffey told a reporter at the time how he had lain in bed, ruminating on the evidence presented to him, and concluded, "I felt sure Hinckley wasn't in his right mind when he shot those people." Coffey was correct (see sidebar: The Hinckley Verdict) and a great deal of human misery would have been saved if politicians from right to left had listened to voices of clarity such as his. Instead, with Reagan's incision barely healed, politicos across the country lined up to strangle the insanity defense and, in four states (Idaho, Montana, Utah and, later, Kansas) to abolish it altogether. In 1984, the federal government hopped on board with its own draconian insanity defense statute.
Modern insanity defense ("insanity" is a legal term, while "mental illness" is the proper psychiatric expression) statutes date back to the M'Naghten Rule, which found its way into Scottish law in 1843. According to the M'Naghten Rule, a person can be found not guilty by virtue of insanity if he or she was unable to tell the difference between "right and wrong" when the crime was committed. ...
via www.truthout.org