ALBANY – A man who thought he was King Arthur and killed his victim after escaping from a mental institution is entitled to a third trial, an appellate panel in Albany ruled yesterday.

For the second time, the Appellate Division, Third Department, said William Demagall was denied a fair trial on his insanity claim and sent the matter back to Columbia County, this time due to conflicting and potentially biased testimony of the prosecution’s psychiatric expert.

Demagall has been convicted twice of second-degree murder in connection with a February 2009 attack in which he repeatedly stabbed his victim with a pocket knife, then bludgeoned him to death with a glass paperweight he had inserted into the toe of a sock before setting the “soulless” body on fire.

The first conviction was overturned in part because of a trial judge’s misapprehension of the law and conclusion that if an individual knows something is illegal then he necessarily knows it is wrong. The judge’s conclusion undercut the defense claim that Demagall lacked capacity to appreciate that his conduct was wrong.

The second conviction was overturned in part because the prosecution’s rebuttal witness, a psychiatrist, wrote an award-winning article praising the later discredited reasoning of the judge.

Records in People v. Demagall, 105720, portray a man on a downward psychiatric spiral for more than a decade who was targeted for involuntary commitment when he fled an institution and committed the 2009 murder.

In 2003, when Demagall was 20, he quit his job, took to carrying a sword and claimed to be King Arthur in search of the Holy Grail, according to the decision.

Over the next several years, he was in and out of mental hospitals as his mental condition deteriorated and he increasingly identified with Arthurian legends—wearing only black, tattooing his forehead with a marking of Merlin, fasting for 40 days and making plans to live in a cave.

Demagall’s family grew increasingly concerned for his safety and that of others and hospitalized him in February 2009. Demagall was in the process of being involuntarily confined when, on Feb. 9, 2006, he escaped from a secure unit and committed the instant offense.

The defendant provided police with a lengthy account of the premeditated murder, which he dubbed “Operation Cobra” that required eliminating a snake— namely, the victim.

Demagall and the district attorney agreed to a bargain which would have allowed the defendant to plead not responsible by reason of mental disease or defect.

The proposed bargain was based largely on the findings of a psychiatrist who had examined the defendant at the prosecution’s request and concluded that while Demagall could understand that murder was illegal, he did not appreciate that such conduct was morally wrong.

Then-Columbia County Judge Paul Czajka, who is now district attorney, rejected the plea bargain. He interpreted the law to state that if a defendant knew his conduct was illegal then he had to know it was wrong. The Third Department reversed him in 2009 (63 AD3d 34) and ordered a new trial before a different judge.

At retrial before Columbia County Judge Jonathan Nichols (See Profile), three defense psychiatrists and the prosecution’s expert all agreed that Demagall had suffered from a mental disease or defect at the time of the crime. The defense witnesses based their conclusion in part on Demagall’s assertion that he had received a delusional “vision” and was on a mission from God.

Psychiatrist Alan Tuckman, who testified in rebuttal for the prosecution, opined that Demagall was malingering by citing conversations with a treating psychiatrist who did not testify. His conclusion was directly at odds with his opinion of Demagall’s mental state at the 2006 trial.

Additionally, Tuckman was allowed to testify about an article he had written, and for which he received an award, lauding Czajka’s later-overturned opinion that someone who knows an act is illegal by definition knows it is wrong.

In its decision Thursday, the Third Department said Nichols had wrongly restrained defense attorney Richard Mott (now a Supreme Court justice) in cross examining Tuckman. As a result, the jury was left “with an inappropriate and unwarranted impression that Tuckman’s opinion, by virtue of his article and award, was more worthy of belief and acceptance than that of other experts who testified at trial.” It also said the court wrongly admitted records from the mental institution where Demagall was detained and hearsay testimony of the treating physician.

Writing for the unanimous court, Justice Leslie Stein (See Profile) said that “this was a very close case on the issue of defendant’s sanity at the time of the murder,” and “with the scales so delicately balanced” the errors gave prosecutors an unfair advantage.

“While County Court did give the jury limiting instructions at certain points when the records and statements were being used, no such instructions were given at the point at which this evidence was most damaging to defendant’s case,” Stein wrote in an opinion shared by justices John Lahtinen (See Profile), William McCarthy (See Profile) and Elizabeth Garry (See Profile).

Paul Connolly, an attorney in Delmar who represented Demagall on appeal, said he is gratified his client will get another chance at trial but noted there are no victors in this type of case.

“This is a situation where the defendant would not have committed the offense if he did not suffer from mental illness, yet that is not a defense,” Connolly said, noting that the standard is not whether the defendant is ill but whether he understands the consequences of his actions and knows right from wrong. “I’m sure it is very hard on the victim’s family. I know it is very hard on Mr. Demagall’s family. It is just terrible for everyone.”

Michael Cozzolino, special prosecutor, was not immediately available for comment.