It is
easy to believe that any rapist, murderer, pedophile, armed robber or violent criminal is insane. Obviously, they must have a few screws loose if they are able to maim and kill without remorse. Legal insanity, however, is much different from the psychological definition, and it is important for juries and even the general public to understand the distinction.
In order for a criminal to be punished for his or her crimes, the prosecutor must establish at trial that he or she possessed the mental capacity to justify intent. In other words, he or she set out to commit a crime, then followed through with it. Without intent, a
crime is not considered a
crime at all, though the perpetrator will likely serve time in a mental institution until physicians declare he or she capable of returning to society. This is the premise for
legal insanity, which is very difficult to prove.
Although each state has its own definition of
legal insanity, the main basis for this defense is fairly universal. In order to prove that a criminal was legally insane, the defense must establish that a mental
disease or defect rendered him or her incapable of appreciating the nature and consequences of his or her actions.
For example, a murderer diagnosed with paranoid schizophrenia might fit the definition of
legal insanity if he committed his
crime because the voices in his head convinced him that the victim was a threat to his life. The victim might not have presented any such threat, but because he genuinely believed it to be true, he can't be held responsible for his actions.
In many cases,
legal insanity is determined as a result of a 730 exam, which is ordered by the courts. This examination, which is conducted by a state-appointed psychologist, can determine whether or not the defendant is capable of standing trial for his crimes, or to determine if an insanity defense has any merit in a court of law.
source...
http://www.associatedcontent.com/article/546475/what_is_legal_insanity.html