ROCKLAND — A Knox County jury deliberated for three hours Friday afternoon before convicting a Tenants Harbor man of murder in the shotgun slaying of his friend 14 months ago.

Andrew J. Kierstead, 41, faces a minimum of 25 years in prison with a possibility of life behind bars. Kierstead admitted shooting his friend, but his defense lawyer had asked the jury to find his client guilty of the lesser charge of manslaughter based on his state of mind at the time.

Kierstead showed no emotion after the verdict was announced at 5 p.m. in Knox County Superior Court.

Justice Jeffrey Hjelm said sentencing could be held in late February. Kierstead has been held without bail since his arrest the night of Sept. 27, 2012, when he shot 48-year-old Richard L. Mills outside the victim’s house on Far Meadow Lane in Cushing.

The judge instructed jurors that Kierstead had to have intended to kill Mills for them to find Kierstead guilty of murder.

Assistant District Attorney Leane Zainea concluded her closing arguments by saying that the evidence was clear that Kierstead’s intent was to kill Mills.

“His opiate addiction is not an excuse for murder,” Zainea said in wrapping up her argument.

During their deliberations, jurors asked to have a portion of a taped interview by police of Kierstead replayed. In that section of the interview, Kierstead reluctantly admitted that he intended to kill Mills when he shot him.

During her closing argument, the prosecutor also had detailed the forensic evidence from the chief medical examiner and a firearms expert on how Kierstead shot Mills and followed the victim to continue firing four more shots with a 12-gauge shotgun.

“He didn’t shoot wildly. Instead, he leveled the shotgun at Richard and fired,” she said.

Defense attorney Steven Peterson continued to argue, however, that the shooting death was not murder but instead the lesser crime of manslaughter. He said Kierstead was too intoxicated and suffering from years of opiate addiction and — on the day of the shooting — from opiate withdrawal to have formed the intent to kill the man who had been providing him drugs for more than a decade.

Peterson repeated statements made by his client to officers on the night of the shooting in which Kierstead kept saying he didn’t know why he shot Mills.

“He told the officer that he couldn’t believe what he did. Those are not the words of someone who intended to kill someone,” Peterson said.

Many of the witnesses who testified for the state and for the defense since the trial began on Tuesday were the same people who testified at a suppression hearing earlier this month. The defense had tried unsuccessfully to get Kierstead’s statements to police thrown out.

On Friday, an emergency room nurse and an emergency department physician testified about treating Kierstead in the early morning hours after the shooting..

Both said that Kierstead was suicidal. The defendant’s blood alcohol level was 0.54 at 1:30 a.m., about 12 hours after the shooting.

Testimony showed that on Sept. 27, Kierstead started drinking heavily as soon as he awoke in the morning. He stopped at a bottle redemption center in Thomaston to return some bottles to buy beer and then called Mills in hopes of getting more drugs.

Mills refused to provide Kierstead any more drugs, however, until he paid a $250 debt, and an argument ensued, according to statements made by Kierstead to police. Later in the day, Kierstead went to Mills’ home and Mills went outside to help Kierstead repair his truck. That is when Kierstead took the loaded shotgun out of his vehicle and shot Mills, according to police.

A neighbor reported hearing gunshots about 1:30 p.m.

On Friday morning, Justice Jeffrey Hjelm announced that one male juror had been excused because of an illness. There was no problem since two alternates had been picked for the jury.

Hjelm also said that a female juror would remain on the panel even though she appeared to have fallen asleep.

“It appears for a quite brief time she was not with us,” the judge said. He said neither attorney requested that she be taken off the jury.