A Sonoma County man was convicted of first-degree murder Wednesday for gunning down his sister's boyfriend last year in the couple's Alexander Valley home.

Jurors rejected arguments that Jarrod Miller, 30, was acting in self defense and suffering mental illness when he shot Timothy Neuer, 29, as Mandy Miller watched in horror.

The ex-Marine, who was also found guilty of residential burglary and firearm enhancements, showed no reaction as the verdict was read. He now faces a maximum 50 years to life plus 16 years in prison at his April 27 sentencing.

"Justice was served," said District Attorney Jill Ravitch, who tried the case alongside deputy prosecutor Scott Jamar. "The jury did an excellent job."

The victim's family and the seven-woman, six-man jury left without making any comment.

The verdict followed two days of deliberation in a trial that opened Feb. 10.

Witnesses described Miller as a troubled man who grew up on the Russian River and drifted around after being kicked out of the Marines in his early 20s.

After spending several years in Las Vegas, Miller returned to the area in 2010 and became financially dependent on his sister, who let him live with her and Neuer.

But the couple tired of Miller, described by witnesses as a "mooch," and asked him to move to another home they rented in Cloverdale.

Miller became angry and began planning Neuer's "execution," prosecutors said. He rented a car, drove to Nevada and bought a handgun at a sporting goods store.

On March 8, 2011, within days of the purchase, Miller showed up at the couple's Alexander Valley home, asked to talk with Neuer, and then shot him three times when he emerged from a bathroom.

Afterward, Miller turned to his sister and said, "It's going to be OK," before calmly walking out the door.

He was arrested a few miles away on Old Redwood Highway after his sister called police. The .380-caliber semi-automatic pistol he bought at a Cabela's store was lying near the shoulder of the road.

Miller's lawyer, Joe Bisbiglia, never denied that Miller shot Neuer. But he argued Miller was motivated by fear that Neuer might hurt him and mental illness described by a defense expert as paranoid schizophrenia.

Compounding Miller's worries was the fact Neuer had a large marijuana growing operation that was "a recipe for violence," Bisbiglia argued.

In closing arguments, he asked jurors to return a verdict of voluntary manslaughter.

But Ravitch argued Miller's actions showed premeditation and deliberation. She said Miller tried to prevent losing control of his sister to Neuer so he went to their house with a loaded firearm, "ready to do evil."

Holding a toy gun during her closing argument, Ravitch described Miller firing a first shot, pushing his sister away as she tried to stop him, and then firing two more bullets. One hit Neuer in the head.

"He was on a mission," Ravitch said. "And he carried that mission out."