Defendants charged with criminal offenses in New Jersey can raise a variety of defenses. These are specific claims or arguments asserting that, even if the allegations against the defendant are correct, the defendant is not criminally liable. Many defenses are derived from the common law, and the New Jersey Code of Criminal Justice (CCJ) also defines various defenses. Since driving while intoxicated (DWI) is an offense under the Motor Vehicle Code, rather than the CCJ, courts have addressed whether common-law defenses are available in DWI cases on a case-by-case basis. The insanity defense involves the claim that a defendant was incapable of understanding the wrongful nature of their conduct at the time. A Law Division court considered the question of how this might apply to a DWI case at some length in State v. Inglis in 1997.
Insanity is a common-law affirmative defense in New Jersey. When a defendant raises a defense in a criminal case, the prosecution must rebut the defense as a part of their burden of proving guilt beyond a reasonable doubt. An affirmative defense, however, partially shifts the burden to the defendant, who must prove the elements of the defense by a preponderance of the evidence.
New Jersey uses the M’Naghten rule to identify what a defendant raising the insanity defense must prove in court. The rule derives from an 1843 English case in which the defendant killed the British Prime Minister’s secretary, falsely believing that the secretary was involved in a conspiracy against him. Under this rule, everyone is presumed to be sane, unless they can prove that, at the time of the offense, they suffered from a “defect of reason” or “disease of the mind,” which kept them from either “know[ing] the nature and quality of” their actions, or from “know[ing] what [they were] doing was wrong.” This is, by design, a difficult standard of proof.