Jurors starting deliberations Monday in the trial of a man accused of gunning down his sister's boyfriend were asked to decide if it was a calculated act by someone bent on murder or a case of self-defense, clouded by mental illness.

It was never in dispute during six days of testimony that Jarrod Miller, 30, killed Timothy Neuer, 29, in the Alexander Valley home Neuer shared with Miller's younger sister, Mandy.

But both sides disagreed on the motive and Miller's state-of-mind.

District Attorney Jill Ravitch, trying her first case since her 2010 election, said in closing arguments that Miller was unhappy about losing financial support from his sister and developed a scheme to "execute" the man he saw as the cause.

He drove a rental car to Nevada, bought a handgun and returned to Sonoma County with it, Ravitch said.

Within days of the purchase, Miller came to Neuer's house, stood in his living room and shot him three times, including once in the head.

In a calm voice, Miller then turned to his sister, who was a witness, and said, "It's going to be alright," and left, Ravitch said.

"That is first-degree murder, ladies and gentlemen," Ravitch told jurors.

Miller's lawyer, Joe Bisbiglia, offered a different take on Neuer's death and asked jurors to consider a lesser charge of voluntary manslaughter based on a form of self defense.

Miller bought the gun not to kill Neuer, but to protect himself if someone tried to steal the marijuana Neuer was growing at his Alexander Valley house and his mobile home in Cloverdale where Miller was staying, Bisbiglia said.

Bisbiglia described the pot operation as a commercial endeavor worth hundreds of thousands of dollars a season. The Cloverdale garden was 65 plants and Miller lived there by himself, Bisbiglia said.

He refused to take part in either grow, Bisbiglia said.

"When you have marijuana like that, with the ability to get quick cash, it's a recipe for violence," Bisbiglia said.

Adding Miller's fear of a home-invasion robbery was a longtime mental illness that an expert diagnosed as paranoid schizophrenia.

On the night of the March 8 killing, Neuer and Mandy Miller had confronted Miller in Cloverdale about financial matters.

Two hours later, Miller drove to Neuer's Alexander Valley house to discuss their differences, Bisbiglia said.

Neuer stormed out of a bathroom and towered over Miller, who was sitting on a couch. Possibly fearing he would get killed or injured, Miller pulled the gun and fired it at Neuer.

Bisbiglia asked jurors to reject first- or second-degree murder in favor of voluntary manslaughter.

"Remember it was Tim who was angry at Jarrod, not the other way around," Bisbiglia told jurors.