A temporary insanity plea is plea submitted by someone accused of a crime that suggests the person was not guilty for several reasons. First the defendant was diminished in mental capacity and could not understand the nature or quality of his behavior. Second, the defendant could not differentiate between basic ideas of right or wrong when he acted in a criminal manner. Since this condition was temporary, it means the person is no longer insane, but was at the time a crime took place. Should a person be judged not guilty because of a temporary condition, he or she may be released without incarceration of any type, whether at a mental hospital or prison.
Some states no longer make a distinction between a temporary insanity plea and an insanity plea. A person may make a plea of not guilty by means of insanity or diminished capacity, and then use evidence that the altered mental state was one of a temporary nature during sentencing. It can be difficult to prove temporary insanity since the defendant is usually no longer considered insane. Information for temporary altered mental state must be gathered in hindsight, and reconstructed from a person’s behavior during the time that a crime was committed. Witnesses who can vouch for the insanity of a person at the time of the crime are invaluable, since they lend credibility to a person’s plea.
In the US, the temporary insanity plea was used in 1859 for the first time. It was successfully argued that Daniel Sickles, a US Congressmen, was insane when he killed his wife’s lover. The temporary insanity plea quickly became associated with crimes of passion, but it still is used less than is commonly thought. Most cases with a temporary insanity plea occurred during the mid 20th century, and the plea is seldom used now. In fact insanity pleas in general are used much less often than people would suppose. They only occur about 1% of the time in court pleas from violent offenders and tend to result in a positive verdict for the defense in about a fourth of these cases.
One of the reasons that the temporary insanity plea has fallen out of favor is that most juries feel that even a person in exceptional emotional pain, as when finding out about an adulterous spouse, or from perhaps losing a child, is probably capable of distinguishing right from wrong, and understanding his/her acts. Temporary insanity, especially in the latter case, is often seen as a thinly veiled excuse for vigilantism. A desire for revenge doesn’t necessarily make a person insane, and people can point to countless examples of others who have suffered losses and not decided to kill or injure people who were responsible for these losses.
The plea may work better if the person judged insane at the time of the act had little motive for their actions. For example a person with a diagnosed mental disorder like paranoid schizophrenia, who is now under treatment and considered sane would have a better chance of arguing temporary insanity, especially if the defense can establish mental disorder diagnosis in the past. If the person is currently sane because of treatment, it might seem inappropriate to sentence him/her to jail time, as long as the condition is not likely to recur and the person is compliant with treatment.