A New York state judge reversed a manslaughter conviction against a man who says he mistakenly killed his friend, ordering a retrial after it was revealed his then-attorney concealed information he obtained about the trial judge's concerns with the defense's case.

Acting Albany Supreme Court Justice Roger D. McDonough on Tuesday vacated Gregory Thayer's 2023 manslaughter conviction, ruling that Thayer's bench trial had been tainted by his local defense attorney's "malfeasance" and the "unexcusable breach" of his duty of loyalty to his client.

In particular, it was discovered that Thayer's local co-counsel, Andrew Kossover, had kept him in the dark about an ex parte meeting he had with a law clerk working for Ulster County Judge Bryan Rounds, who was set to preside over Thayer's bench trial, Justice McDonough's opinion said.

In that conversation, Kossover learned the clerk had doubts, expressed on behalf of Judge Rounds, about the strength of the defense team's temporary insanity theory, and that he suggested an extreme emotional disturbance defense theory could be more persuasive to a jury, according to a statement Thayer filed in his bid for a new trial.

However, Kossover kept this information from Thayer's lead counsel, Robert C. Gottlieb, because, he said, the law clerk had sworn him to secrecy.

In his ruling Tuesday, Justice McDonough slammed Kossover's "reticence and silence," saying it "clearly constituted an inexcusable breach of Kossover's duty of loyalty to his client." He said it is "axiomatic" that had Thayer timely had the information possessed by Kossover, he would have reconsidered the decision to waive his right to a jury trial and might have requested his case be heard by a new judge.

He further noted that Kossover's sole explanation for his "unconscionable dereliction of duty was his desire to maintain his good relationship with the trial judge and the law clerk."

"Kossover's malfeasance," the judge said, "tainted the trial."

The underlying charges in the case stem from Thayer's fatal shooting of his childhood friend Bruce Swierc on the night of Sept. 28, 2021.

Thayer was charged with murder and manslaughter in the first degree. But his attorneys say Thayer killed Swierc by mistake, believing him to be a burglar after a night of booze and drugs. A psychiatrist later testified that Thayer experienced a "psychotic break" after mixing Xanax and alcohol.

Thayer, who waived his right to a jury trial, was convicted in May 2023 by Judge Rounds of manslaughter in the first degree. He was later sentenced to 25 years in prison.

Days after the trial, Thayer's lead attorney Gottlieb discovered Kossover's meeting with Judge Rounds' clerk. Thayer moved for a new trial. Judge Rounds recused himself and Justice McDonough took over the case.

In March, Justice McDonough ordered an evidentiary hearing to probe whether the ex parte meeting compromised Thayer's right to effective counsel under the Sixth Amendment of the U.S. Constitution so severely as to warrant a new trial.

The law clerk, who did not testify at the hearing, said in a declaration that the conversation with Kossover was an effort to facilitate plea negotiations due to a backlog of cases. He denied that it was initiated by Judge Rounds and said he had not asked Kossover to keep it a secret.

Justice McDonough on Tuesday held that the meeting constituted "an improper ex parte meeting" and that Thayer had established his entitlement to a new trial on the grounds of "ineffective assistance of counsel attributable to Mr. Kossover." Thayer, the judge said, had established "the lack of a knowing and intelligent waiver of his right to a jury trial, occasioned by the occurrence, content and untimely disclosure of the ex parte conversation."

Justice McDonough noted that he found Kossover's testimony that he didn't reveal the occurrence or contents of the ex parte meeting to Thayer's lead counsel credible, writing, "Kossover's credibility on this point is buttressed by his stunning admission to the ethical/constitutional violations in which he engaged with no possible, concomitant, personal benefit arising from said testimony."

Thayer must be afforded a new trial, the judge said, even though the second trial will "no doubt cause additional pain and suffering to the decedent's family and friends" and "will require the expenditure of significant judicial, prosecutorial, defense and family resources."

Kossover, the former chief public defender of Ulster County and former president of the Ulster County Bar Association, did not respond to Law360's request for comment Wednesday. As of publication, no record of public discipline appeared on Kossover's New York law license.

Gottlieb, Thayer's lead attorney, told Law360, "We are very grateful for Justice McDonough's decision to vacate the conviction and order a new trial."

Justice McDonough's "carefully analyzed opinion upholds the sacred principles of justice that ensure that everyone is entitled to a fair trial. Unfortunately, our client was not afforded that right," Gottlieb further said.

Another lawyer for Thayer, Joel Rudin, told Law360 Wednesday that while they have not been able to reach Thayer in prison and don't know if he's learned about the court's decision yet, "I have no doubt he will be relieved and thrilled."

Rudin said the court's decision "is the product of a highly unusual set of facts, but it is important for its emphasis on an attorney's fundamental obligation to exclusively serve the interests of his client. Justice McDonough's conclusion that the defense attorney's error here served to deny Mr. Thayer a fair trial is undoubtedly correct."

"The crime charged against Gregory Thayer is one that in his right mind he would never have committed. Having gotten to know him during the [motion to vacate judgment] proceedings, I'm excited that his conviction is now vacated, and he will have another opportunity to show that, due to his mental infirmity, he is not legally responsible for the awful tragedy that occurred," Rudin said.

Counsel for the prosecution did not immediately respond to Law360's request for comment.

Gregory Thayer is represented by Robert C. Gottlieb of Robert C. Gottlieb & Associates PLLC and Joel B. Rudin of the Law Offices of Joel B. Rudin PC.

The Ulster County District Attorney's office is represented by Emmanuel C. Nneji.

The case is People v. Thayer, case number 70188-21, in the Supreme Court of New York, Albany County.

--Additional reporting by Marco Poggio. Editing by Jay Jackson Jr.