On Tuesday evening, beneath a cloud-veiled full moon, Ken Neville exited through the glass front doors of the Marin County Jail, newly freed. After two weeks of trial in Superior Court, it had taken less than a day for jurors to arrive at a verdict: not guilty.

“I’m shocked,” he said, before he was shuttled away to a family home in San Leandro. “I did not expect this.”

Mr. Neville, a soft-spoken 56-year-old white man, faced voluntary manslaughter charges for the shooting

death of a 19-year-old black man, Stachaun Jackson, last spring in Dillon Beach. The single shot was fired in self-defense, Mr. Neville claimed, at the end of a heated domestic dispute between the victim and Mr. Neville’s roommate, Eric Gillespie, in the witching hours of March 20.

Four days later, Mr. Gillespie had committed suicide in Tehama County, leaving Mr. Neville as the sole living witness of the tragic evening.

“We’re very happy,” said Mr. Neville’s sister, Deirdre, as she waited for her brother to be released from jail. “And he’s our hero.”

She pointed to his attorney, Public Defender Michael Coffino, an Inverness resident, exhausted and slumped against a rotary payphone in the jail’s waiting room. Through numerous pieces of evidence, several key witnesses and an hour-and-a-half closing statement, Mr. Coffino succeeded in convincing the jury that his client had acted in self-defense.

“The issue in this case is that Ken Neville believed Stachaun Jackson was intent on harming him,” Mr. Coffino said during his closing statement on Tuesday. “When you’re in your own home, you want to believe you’re safe. And you’re allowed to protect yourself against an intruder.”

According to testimony presented during the trial, 51-year-old Mr. Gillespie, also white, had been seeing Mr. Jackson intimately after the two met at a Hayward bar in late 2012. The following June, Mr. Gillespie and Mr. Neville, who had been roommates for nearly 14 years, moved into a mobile home at Lawson’s Landing, a campground and trailer park in Dillon Beach. It was there the fighting between Mr. Gillespie and Mr. Jackson, a regular visitor, grew violent.

On several occasions the roommates called sheriffs. Once, in July 2013, deputies arrived to find that Mr. Jackson, who earlier had hit Mr. Gillespie multiple times, was locked in the trailer’s bedroom, threatening to kill himself with a knife. Similar disturbances led the two older men to keep a loaded Smith and Wesson .38 Special in an unlocked compartment near Mr. Neville’s bed.

“I was tired of it,” Mr. Neville said last Wednesday on the witness stand. “I was sick of the fighting.”

During the trial, Mr. Coffino displayed several “apology” emails and texts sent by Mr. Jackson to the roommates. “I’m sorry I hit you the way I did, Eric,” one message read. “I love you. I should have never hit you like that.”

The last fight of Mr. Jackson’s life erupted for unknown reasons at around 9 p.m., when he arrived carrying groceries and began to argue with Mr. Gillespie in the bedroom, according to the defendant’s testimony. 

Mr. Neville said Mr. Jackson left the trailer several times, hoping to retrieve guns he believed were stored in a locked container outside.Mr. Jackson choked his lover to find out where he had hidden the keys, so that the young man could regain entry into the mobile home should he be locked out. (He got them.) On this last venture outside, Mr. Jackson forgot to take the keys. (His own car keys were also inside.) According to Mr. Neville, he stalked around the trailer, demanding to be let in while the two men called 911.

In her closing statement, the prosecuting attorney, Cassandra Edwards, countered that Mr. Jackson had either wanted to simply retrieve his own car keys and leave for good, or to resolve the argument with Mr. Gillespie. It had been a cold night, she argued, and Mr. Jackson had been locked outside, unable to leave and unable to keep warm.

“There were no attempts to get the guns,” said Ms. Edwards, whose closing statement lasted only half an hour. “There is no evidence of Jackson running around to get inside.”

What is known is that, suddenly, Mr. Jackson entered into the mobile home through a window. Mr. Coffino showed a photo of a wound on Mr. Jackson’s hand, the skin beneath the nail peeled back, evidence that the young man had wedged open the window and “crashed” through the blinds, which detectives found bent in several places.

“Can you imagine the level to which Mr. Neville’s fear would have increased then?” Mr. Coffino asked. “We depend on the illusion that the walls of our home are in place to keep us safe. At that moment, for these two men, that illusion and that safety was broken, and Jackson became an intruder.”

In his testimony, Mr. Neville claimed that Mr. Jackson had grabbed a kitchen knife and demanded that the two men cancel the 911 call, which they did. What exactly unfolded next is unknown, but, somehow, Mr. Neville took possession of the Smith and Wesson, announced he “had a gun” and told everyone to go outside.

Ms. Edwards, however, argued that much of the defendant’s story was false: the knife-wielding, the gun-searching, the young man’s compliance. Instead, she argued, Mr. Neville had seized the opportunity to end the fighting and the relationship of the two odd-aged lovers, because he did not like Mr. Jackson.

“Ladies and gentlemen, this man had a motive,” Ms. Edwards said. “A 19-year-old kid was killed for no other reason than dislike. How cruel. How despicable. And how horrible that the defendant has tried to describe this kid as a monster.”

Mr. Neville shot the teenager sometime around 2:45 a.m. According to testimony, Mr. Jackson refused Mr. Neville’s demands to “get on the ground” and stop moving. Instead, Mr. Neville claimed he had lunged forward.

“This was the point at which danger was imminent,” Mr. Coffino said. “He realized that Jackson did not have the same risk-factoring that a normal person does. And he didn’t shoot Jackson until after he had taken several steps.”

But during her Wednesday cross-examination of Mr. Neville, Ms. Edwards seemed to have caught the defendant in a contradiction. First, he told detectives on the day of the shooting that Mr. Jackson did not take a step toward him; during the trial, he flip-flopped and told the jury that, yes, Mr. Jackson had taken a step.

“You emphatically told [detectives] that he did not take a step. Isn’t that true?” Ms. Edwards asked.

“Yes,” the defendant replied.

“But today it is true that he did take a step?”

“Yes.”

“So your story has changed.”

“Yes.”

Ultimately, despite the inconsistencies in Mr. Neville’s testimony, Mr. Coffino was able to prove to the jury, “beyond a reasonable doubt,” that the defendant had met the three main criteria for self-defense: that he had been in imminent danger of bodily harm; that the use of immediate force was necessary; and that only enough force was used to deter the threat.

“We don’t convict people in this country on evidence that is as weak and circumstantial as [what Ms. Edwards has presented] in this case,” Mr. Coffino concluded. “Given all the realities of this case, Mr. Neville is not guilty. That is the verdict I’m asking you to return.”

The jury unanimously obliged. 

Judge Andrew Sweet presided and kept an orderly courtroom, save for one cell phone that rang during Mr. Neville’s cross-examination.