As a forensic psychiatrist who has evaluated approximately 200 defendants vis-à-vis insanity, it is my experience that it is difficult to explain a psychotic state to a jury.
At a recent conference about psychiatry in the digital age, I realized video gamers live in an altered reality while playing video games, analogous to a psychotic state, where killing opponents is a central task in the video game. These games have rules which do not include the knowledge of wrongfulness. I believe analogizing this common experience of video gamers who have a psychosis and the M’Naghten1 insanity criteria (and variants) would be a meaningful, understandable way for juries to visualize and conceptualize how a psychotic person can live in an altered reality, where the wrongfulness of killing others is not part of that reality, but nevertheless continues to possess an ability to plan and deceive victims.
The game of chess is an analogous non-digital example: Chess players speak of “killing” an opponent’s chess piece but do not experience wrongfulness or guilt. If asked if it is wrong to “kill” a pawn, bishop or king, the response would be “There is no wrongfulness because that’s what the game is about.”
If a defendant is in the midst of a psychosis where wrongfulness does not exist or is inaccessible, then the knowledge of wrongfulness or illegality similarly does not exist. If a voice (or voices) or a delusion causes the person to act and commit a homicide during this state of mind, then the knowledge of wrongfulness, including the ability to adhere to the law, is absent and, thus, the perpetrator is deprived the ability to know right from wrongboth morally and cognitively.
The insanity defense is rarely employed in homicides; about one in 1,000 homicides result in an insanity defense being raised. When an insanity defense is raised, approximately 20% of the defenses are successful. Thus, one in 5,000 homicides results in a Not Guilty by Reason of Insanity (NGRI) verdict in the United States.
1 M’Naghten Rule [is a] common law formulation of the insanity defense, still in force today, with variations, in many jurisdictions. Under this test, the defendant will be found not guilty by reason of insanity if he or she can show a mental disease or mental defect rendered him incapable of understanding the nature of his or her actions, or of distinguishing between right and wrong regarding the crime with which he or she has been charged. Online resource: https://www.law.cornell.edu/wex/m%27naughten_rule