Insanity, Incompetence, And Diminished Capacity: What's The Difference?

What happens if someone with a mental impairment is accused of a crime? There are three possible ways that a defense attorney can bring a defendant's cognitive issues into court, each with different results. If someone you care about suffers from a mental disorder and is accused of a crime, it's important to understand the difference between legal insanity, incompetence and diminished capacity.

What is legal insanity?

Insanity doesn't prevent a trial or a verdict. Instead, a defense of legal insanity admits that the defendant committed the crime but asserts that his or her mental state at the time of the crime as a valid excuse for whatever action led to the charge. Depending on the state, a person might have to prove that they were in the grip of an "irresistible impulse" that caused them act, despite knowing the action was wrong. In other states, they have to show either that they didn't know the difference between right and wrong or cannot conform their behavior to the law.

If someone is found "not guilty by reason of insanity," he or she will not be released into the public. Instead, he or she will be sent to a secure mental health facility until mental health professionals determine that he or she is no longer insane and no longer a threat to others. Someone could end up being detained for a lifetime, like John Hinkley Jr., or for only a few weeks, like Lorena Bobbitt.

What is incompetence?

Incompetence prevents prosecution altogether, but it isn't a defense. An allegation of incompetence means that a person's current mental state is so diminished that he or she can't understand the proceedings and can't assist in his or her own defense. That makes it fundamentally unfair to put the defendant on trial, so guilt or innocence can't be determined.

Historically, the mobster Vincent Gigante delayed proceedings against himself for decades by pretending to be chronically insane (and therefore, incompetent). In a current case, former pro wrestler Jimmy Snuka's trial for the 1983 murder of his mistress is on hold because the now-elderly Snuka is showing signs of dementia. In cases like Snuka's, incompetence may be a permanent condition.

In many cases, however, incompetence is a fleeting thing that can be caused by a temporary breakdown or other mental condition that can be treated. Once the defendant's condition is successfully treated, his or her trial can resume. 

What is diminished capacity?

Diminished capacity is essentially an argument for leniency. Diminished capacity is similar to the insanity defense in that it addresses the state of mind of the defendant during the criminal act. It argues that the defendant should be considered guilty of a lesser offense than charged because he or she lacked the mental capacity to form the intent necessary to be guilty of a more serious charge. It does not mean that he or she is entitled to an acquittal. It also might have nothing to do with insanity, since almost any mental condition that affects someone's thought processes could be used to argue diminished capacity, including low blood sugar, mental retardation, or ordinary depression.

For example, attorneys for Dan White successfully argued that his depression prevented him from clearly planning the killings of two San Francisco politicians. As a result, he was convicted of manslaughter instead of murder.

To discuss the possibility of any of these three mental states coming into play during a trial, talk with a criminal law attorney near you.