Teenager Mark Devlin (John Wildman) shoplifts a curved linoleum knife from a hardware store and then, seeing a customer pay for a television set in cash, follows the stranger to the parking lot.
He attacks and brutally kills the man impulsively during the robbery by slitting his throat in full view of multiple witnesses and the victim's five-year-old son, who watches in stunned silence.
At the time the film was made, s. 16(2) stated: "a person is insane when he ... has a disease of the mind to an extent that renders him incapable of appreciating the nature or quality of the act.
"[2] For the Record was intended as a series of dramas which would take an honest look at problems in Canadian society, among them many about mental illness and "flawed social institutions".
[5] Gail Henley remarked in 1985 that For the Record dramas were "information laden" when compared to their more emotional American counterparts and emphasises the importance of research and documentation for the series.
"[2] By Reason of Insanity was first broadcast on 7 March 1982,[7] at a time when revelations of the Clifford Olson serial murders were still fresh in the minds of the audience.
Reviewing For the Record's 1982 season of dramas, Bill MacVicar judged By Reason of Insanity to be the best, "well-crafted" and displaying "praiseworthy equilibrium" and found it "refreshing" that the film withholds editorial judgement:By Reason of Insanity questions the market in "expert" witnesses and the adversarial system itself, but it leaves us with a disturbing paradox.
[3]Wessley Hicks calls the film "a terse, spare, provoking drama", that, while making no judgments, does create uneasiness.
[8] Mike Boone was impressed by John Wildman, who he found projects everyone's "nightmare image of adolescent menace alternately unfeeling and touchingly vulnerable, impulsive and full of pent-up hostility.
"[2] He also found the film as a whole was a "refreshing change" from American TV trial scenes from Perry Mason on down: "No cries of "Objection!"