The purpose of this study was to assess viewpoints about criminal liability as one of the elements of the crime and present the importance of professional expertise on diagnosis of mental illness and physical defects. It is an affirmative defense to a prosecution under current criminal law that at the time of the commission of the acts constituting the offense, the defendant, as a result of a severe mental disease or defect, was unable to appreciate the nature and quality or the wrongfulness of his acts. Mental disease or defect does not otherwise constitute a defense. In criminal trials, the insanity defenses are possible defenses by excuse, by which defendants argue that they should not be held criminally liable for breaking the law because they were legally insane at the time of the commission of alleged crimes. The legal definition of “mental and physical disorder” is, in criminal cases, quite different from psychiatric definitions of it. This excuse is based on evaluations by forensic professionals that the defendant was incapable of distinguishing between right and wrong at the time of the offense. This study suggest the important steps in the direction of examining and analyzing the role of psychiatric diagnosis according to the responsibilities of the evaluator. It is anticipated that there will be further work in these areas to address not only diagnoses but forensic recommendations and opinions.