Articles Tagged with Expert Testimony

The New Jersey Supreme Court has answered a question that has lingered in our criminal courts for decades: can a defendant obtain a diminished capacity jury instruction on lay testimony alone? In State v. Mustafa, a unanimous decision issued on August 3, 2026, the Court held that expert testimony is required both for a defendant to invoke the diminished capacity defense and for a trial court to instruct the jury on it. The Court affirmed the Appellate Division and confirmed that an expert is necessary to support an insanity defense. For anyone who handles serious violent crime cases, this opinion changes how mental health evidence must be developed, and it changes it well before trial begins.

The case arose from a late night shooting on a Monmouth County highway in May 2018. The defendant was driving with his then girlfriend when the victim, traveling on the same roadway, turned on her high beams because one of her headlights was out. The defendant became upset, pulled over to let her pass, then accelerated until he nearly struck her bumper while flashing his own high beams. As her car began to exit, he put his vehicle in neutral, rolled down his window, drew a handgun, and fired. She died of a gunshot wound to the head. A grand jury returned a six count indictment charging first degree murder, weapons offenses, and endangering. Defense counsel initially served notice of an insanity defense, but the defendant later instructed his attorney to withdraw it, and a pretrial memorandum recorded that decision in plain terms, noting that the insanity defense was withdrawn and that there would be no psychiatric expert testimony. The trial court found the waiver knowing and voluntary.

Diminished capacity, however, was raised explicitly at trial, and a fair amount of lay evidence about the defendant’s mental health reached the jury. His then girlfriend testified that he had begun seeing her psychiatrist to obtain Adderall because he liked how it made him feel, that he smoked marijuana daily, and that he had immersed himself in conspiracy research. She described his belief that he was the target of gang stalking, that people were shooting laser beams, radiation, and concentrated microwaves at him, and that he wore tin foil under a baseball cap and helmet to deflect the rays. She said his statements reminded her of a relative who has schizophrenia. On the night of the shooting, she testified, he took Adderall three times within several hours, yelled about people trying to hit him with radiation and follow him, and screamed that he could not take it anymore and had to fight back. The defendant did not testify and called no witnesses. When counsel requested a diminished capacity charge at the close of evidence, arguing that a medical diagnosis was not required, the trial court denied it because there was no medical or expert testimony in the record. The jury convicted on all counts and the defendant received an aggregate life sentence.