GETTYSBURG, Pa.—A man convicted of killing a state game warden during a poaching investigation has been sentenced to death.

The Adams County jury issued its verdict in the penalty phase of Christopher Johnson's trial Thursday night. Jurors had been deciding between giving Johnson life in prison or death in the 2010 killing of wildlife conservation officer David Grove. Earlier Thursday, Johnson had taken the stand and said he was sorry for the pain he had caused Grove's relatives, lamenting there was nothing he could do to bring Grove back.

"I just want to say I'm sorry for the pain I caused your family," Johnson said. "I wish there was more I could do."

On Tuesday, the jury deliberated less than an hour before convicting the 29-year-old Johnson, of Fairfield, of first-degree murder in the November 2010 slaying.

Investigators said Johnson and a friend had poached a deer at night when Grove pulled them over on a rural road near Gettysburg. The passenger said a shootout began after Johnson, a convicted felon, vowed never to go back to prison. Jurors were told the two men fired 25 shots in the exchange, which left Grove dead and Johnson injured.

The defense had sought a lesser conviction, arguing that Johnson was too drunk to form the intent to kill. A doctor who treated Johnson's wounds said the defendant told him he drank 12 beers the day of the shooting.

But prosecutors cited four aggravating circumstances that supported imposing the death penalty, including that the murder occurred during commission of a felony and that the victim was a law enforcement officer killed while performing his duties.

Grove was the first Pennsylvania game warden killed in the line of duty in 95 years, and more than 1,000 mourners attended his funeral.