DOVER, N.H. — A jury Tuesday rejected a defense claim that a Maine man killed a New Hampshire woman three years ago and instead produced a first-degree murder verdict against the man who was on trial.

Edward Pehowic, 33, of Somersworth immediately was sentenced to mandatory life imprisonment. Judge Bruce Mohl said Pehowic deserved it because of the “brutality and depravity of your acts.”

Throughout the late-afternoon announcement, Pehowic’s relatives wept in the row behind where he sat. One brother said, “I love you,” as Pehowic was led from the courtroom to begin his sentence. Relatives of the victim, Carol Caswell, were not in the courtroom; they already had left the Strafford County Superior Court expecting to return today for a second day of deliberations.

Pehowic was convicted of drowning Caswell, a 35-year-old single mother, in August 1996 during an evening of drinking and drug use at Willand Pond in Somersworth. The defense blamed it on Merrill “Mickey” Tompkins, 25, who now lives in Augusta, Maine, but who also has lived in the Maine towns of Lincoln and Island Falls.

The two men met in late August 1996 at the Somersworth hotel where they both were staying. Later that night, they met up with Caswell outside a bar in nearby Portsmouth before driving to the lake.

What was not in dispute was that after the slaying, the two men then drove to Maine and buried Caswell’s body in Lincoln. As the key prosecution witness, Tompkins testified that he helped dispose of the body out of fear.

Eight men and four women returned the verdict in about 3 1/2 hours. Had they acquitted Pehowic, they would have had the option of convicting him on a lesser offense, either second-degree murder or manslaughter.

Afterward, defense attorneys Barbara Keshen and David Rothstein would say only that they planned to appeal the verdict. Assistant Attorney General Patrick Donovan said he was not surprised at how swiftly the jury reached its verdict.

“This was a very strong case,” he said, praising the panel for sifting through “some very difficult evidence.”

Donovan would not say for certain how this conviction would affect other unsolved murders. In a videotaped confession played for the jury, Pehowic also referred to another local murder case. Donovan confirmed he was a suspect in that case, but would not say whether he was suspected in other cases. In any event, said the prosecutor, it may not be worth further prosecuting Pehowic, since he is in jail for life.

“It doesn’t seem to me that it would be practical to go back into court and try to prove that he murdered another woman,” he said.

The jury began its deliberations with diverse images of Pehowic, drawn by the lawyers for both sides during closing arguments. He was, by turns, portrayed as a victim of investigative pressure and a “callous beast.”

Keshen reiterated the defense theme that Tompkins was Caswell’s real killer and that the investigation was flawed.

“The state pursued its investigation with its eyes wide shut,” she said, borrowing the title of a recent film in what would become a recurring theme of her presentation, and the first of two competing movie analogies.

Donovan countered with his own theatrical reference, saying Pehowic had laid his life bare in his videotaped confession, in which he provided “intimate details too twisted to make up.”