For the fourth time in four decades, the fate of Robert Fisher lies in the hands of a jury.

Prosecutors in Montgomery County on Thursday urged jurors to repeat the outcome of previous trials and find Fisher guilty of first-degree murder in the death of his ex-girlfriend, Linda Rowden, in July 1980. But Fisher’s attorney, Carrie Allman, asked for a different outcome and said Fisher, 75, should be acquitted.

“Lies don’t last, and today’s the day that 41 years of lies end,” Allman said in the Norristown courtroom of Judge Todd Eisenberg.

But after seven hours of deliberations Thursday — and multiple questions, including asking for the legal definition of reasonable doubt — the jurors said they were unable to reach a consensus. Eisenberg sent them home for the evening, and they will return Friday morning to continue.

Fisher is accused of shooting Rowden, 26, twice at point-blank range as she drove him through Norristown. Investigators have said at this week’s trial — as they had in three earlier proceedings — that Fisher killed Rowden because she was cooperating with detectives investigating the murder of a federal informant Fisher was suspected of killing.

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In the 41 years since Rowden’s death, Fisher was convicted twice and sentenced to death three times, but those decisions were overturned on appeal by federal judges who said errors by prosecutors and county judges denied him a fair trial. The passage of time affected this week’s proceedings. Many of the witnesses have since died, and prosecutors had to rely on their testimony from earlier trials.

But Allman said that the key witnesses in the case, including Richard Mayo, a friend of Fisher’s who was sitting in the front seat of Rowden’s car at the time of the shooting, were inconsistent and unreliable. He and others changed their stories, she said, amid pressure from police.

Fisher, meanwhile, took the stand Wednesday to tell jurors he wasn’t in the car when Rowden was shot. He said he fell ill while riding in the car with her and got out of the vehicle and walked to a nearby alley, where he vomited.

Allman posited that Mayo was the killer, and wrongly accused Fisher after being spotted by police not far from the scene. She based her theory in part on the evolving statements Mayo gave to police between 1980 and Fisher’s second trial in 1991.

“Why is there no consistent story here? If Richard Mayo was in that car, he should have known what happened,” Allman said. “It is because he was responsible. And when he’s found, what’s the first thing that comes out of his mouth? The easiest and most convenient lie: ‘It was Bobby.’”

Allman asserted that Mayo killed Rowden because of his friendship with Denise Walker, another woman Fisher was dating. If Rowden were dead, she said he reasoned, Fisher would spend more time with Walker, who was infatuated with him.

“The commonwealth is right: 41 years is a long time to wait for justice,” she said. “And I’m asking you today to give justice to Robert Fisher. I’m asking you to find him not guilty.”

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First Assistant District Attorney Ed McCann Jr., the lead prosecutor on the case, disputed that theory of the case.

He said there was “no evidence whatsoever” that Mayo fired the fatal shots, and stressed that Fisher was the only person who had a motive for killing Rowden. Two days before Rowden was killed, McCann told the jury, Fisher assaulted her, and police had a warrant out for his arrest.

“This is not a murder mystery, ladies and gentlemen,” McCann said. “This is not a made-for-TV plot. This is something that, sadly, happens all too frequently, people hurting people they’re involved with.”

McCann noted that Fisher didn’t just flee the scene of the shooting, he “left his life” in Norristown and moved to New York, where he obtained false identification and lived under a fake name for seven years.

“To find him not guilty, you would have to believe all of the witnesses are part of a big lie,” McCann said. “That everyone lied about him being involved with this murder, even though the evidence shows he’s the only one who ever had any issue with Linda Rowden.”