At the time, Mr. Gottlieb said those delusions were evidence that Mr. Comello was unfit to stand trial and instead should be given psychiatric treatment. The judge has since imposed a gag order, and Mr. Gottlieb has declined to comment on the proceedings.

In New York, the legal bar for an insanity defense is high. Defendants must show not only that they have a mental illness, but that the illness prevented them from understanding the consequences of their actions or from knowing they were morally wrong.

Prosecutors have proceeded in court as if Mr. Comello is mentally competent and can be held responsible for his actions. At a hearing in October, the lead prosecutor, Wanda DeOliveira, said that Mr. Comello’s mind was “crystal clear” when he waived his right to a lawyer during his interview with detectives.

She argued that Mr. Comello appeared rational in the interview. He gave careful thought, for instance, to one question and asked for it to be repeated before answering. “If you watch the defendant while he comes into the room — his physical condition, his mannerisms — he waits when he is talked to and spoken to, he responds normally,” Ms. DeOliveira said. “He’s reacting fine.”

Using mental illness as a defense in such a case is not without precedent, Mr. Perlin said. Almost all of the early insanity defense cases were political in nature, he said, going back to the attempted assassination of King George III in 1800.

“You’ve got a real, real tradition of insanity defense cases of very, very seriously mentally ill people who committed their crime out of some kind of utterly bizarre political motivation,” he said.