A man serving 20 years to life for murder will get a new trial because the judge failed to tell jurors that a robbery victim is justified in using deadly force against an assailant who is not presenting a lethal threat.

The Appellate Division, First Department, cited various errors in overturning Kelly McTiernan’s 2010 conviction to second-degree murder. But the key finding in a decision handed down Thursday dealt with the standard for justifiable homicide, and how that standard differs for assault and robbery victims.

In a unanimous opinion, the justices said that while an assault victim can use deadly force only if his or her life is in jeopardy, a robbery victim can use deadly force to confront any physical threat.

The decision in People v. McTiernan, 2014 NY Slip Op 05363, arose from an incident in the early morning hours of Oct. 12, 2007, when the defendant stabbed and killed Fain Upshur in the West Village, apparently in connection with a dispute over a cellphone.

Records show that McTiernan had allowed a friend, Abdul Flynn, to use his cellphone, but it became apparent that Flynn had no intention of returning it. At some point, the victim appeared and then began walking away with Flynn and the cell phone, resulting in a confrontation.

Testimony differed on whether the stabbing of Upshur was provoked or unprovoked. In any case, McTiernan asserted a justification defense, claiming that Upshur lunged at him with what appeared to be a knife. The defendant said he “poked” Upshur in the chest with his own knife in self defense, killing him.

The trial judge, Supreme Court Justice Rena Uviller (See Profile), charged the jury on the law of self-defense under two distinct theories: the use of deadly force to thwart the imminent use of deadly force (Penal Law §35.15); and the use of deadly force to defend against a robbery (Penal Law §35.15). Uviller told the jury that the only difference is that in repelling a robbery, a person has no duty to retreat.

“This is an incorrect statement of law because it ignores an additional critical difference between the two grounds for justification, namely, that deadly force may be permissible to defend against a robbery even if the alleged robber is using only physical force, and not deadly physical force,” the First Department said in an unsigned opinion by justices Peter Tom (See Profile), Dianne Renwick (See Profile), Rosalyn Richter (See Profile), Paul Feinman (See Profile) and Judith Gische (See Profile).

The court said that while parts of the charge were correct, Uviller “misstated the law on the most critical issue in the trial—whether defendant was justified in using deadly physical force.” It said the charge, viewed in its entirety, “was inconsistent and confusing” and “could have left the jury with the erroneous impression that defendant could not use deadly physical force to thwart a robbery unless deadly physical force was being used by the robber.”

Additionally, the First Department said Uviller should have suppressed statements obtained in violation of the right to counsel. According to the decision, McTiernan’s attorney, Glenn Garber of Manhattan, had called police and told them not to question the defendant. The court said Uviller wrongly precluded Garber from testifying at the suppression hearing about his conversation with police.

“The court should not have made a factual finding that implicitly accepted [the police officer's account that the defendant had waived his Miranda rights] without giving defendant an opportunity to challenge that account,” the First Department said.

However, the panel said, that error was harmless since the prosecution did not use the statements in its case-in-chief.

“If, at the retrial, the People intend to introduce defendant’s statements … a new suppression hearing is required,” the court said.

Finally, the First Department said Supreme Court Justice Carol Berkman, who presided over motions in the case but is now retired, wrongly unsealed records of two prior cases in which the defendant was involved in stabbings he claimed were justified. However, absent any evidence that information from those files was presented to the grand jury or used at trial, “defendant suffered no prejudice,” the court said.

Garber argued the appeal for McTiernan and was elated with the ruling.

“For Kelly McTiernan, it is obviously tremendous,” he said. “We felt all along that Kelly was acting in self defense and should have been acquitted. The jury was out for eight days and in my estimation, the erroneous instruction tilted the scales away from an acquittal.”

Garber said the ruling also emphasizes that “in a self defense case, jury charges are of pronounced importance. If a jury does not have the exact tools it needs, it cannot render a just verdict.”

Assistant Manhattan District Attorney Dana Poole appeared for the prosecution. There was no immediate reaction from the district attorney’s office.