PORTLAND – Maine’s highest court Tuesday denied the appeal of a Casco man who was sentenced to 40 years for murdering his longtime girlfriend after a night of drinking.

Gary Sweeney, 46, did not deny that he was holding the gun that killed Christine Pepin on Feb. 4, 2003, but argued that her death was accidental because he failed to realize that his .22-caliber revolver was loaded.

In upholding the conviction, the Supreme Judicial Court rejected Sweeney’s contention that there was insufficient evidence for the jury’s finding that he intentionally or knowingly caused Pepin’s death.

The justices agreed that the prosecution erred in asking Sweeney whether his son, who was 12 at the time, had lied when he testified that his father had “dry-fired” the weapon on the evening of the shooting.

The ruling stated that while the question improperly asked Sweeney to give his opinion of another witness’ veracity, Sweeney did not object to the question at the time, the prosecutor made no further reference to Sweeney’s reply that his son had lied and the error does not require the court to set aside the conviction.

Sweeney said he took the revolver from a drawer and intended to fire a few shots out his front door to signal his neighbor to send his son home to their small cabin along a steep ridge.

He said he then went to the cabin’s sleeping loft, absent-mindedly carrying the gun, which he presumed to be unloaded. When he tried to pass the gun to Pepin so she could put it away, his thumb slipped on the hammer and the weapon fired, shooting Pepin in the head, he testified.

The state noted that the shot was fired from no more than 3 inches from the victim’s head.