Forty-one years and four trials were not enough to settle Robert Fisher’s fate.

On Friday, a mistrial was declared in the latest murder trial against the 75-year-old, who has been in prison for decades on charges he killed his former girlfriend in Norristown in 1980. After deliberating for a day and a half, a Montgomery County jury deadlocked.

Fisher, who has long said he did not kill then-26-year-old Linda Rowden, has had several successful appeals, resulting in a more-than-40-year prosecution.

He leaned forward over the table in Montgomery County Court Friday afternoon as Judge Todd Eisenberg said: “The jury cannot come to a unanimous decision.” Officers escorted him out of the courtroom in handcuffs, walking him past Rowden’s family, whom he did not look at.

Prosecutors plan to try the case again, meaning Fisher is facing a fifth trial — one that likely won’t take place until next year.

Jurors told the judge Friday they couldn’t agree on either first- or third-degree murder charges after asking multiple questions. They twice inquired about the legal definition of “reasonable doubt.” And at one point Friday morning, jurors wrote to the judge: “We have a juror who is unable to follow instructions. Please advise.”

Eisenberg read instructions to the group once more, and sent them back into deliberations. An hour later, they said there was no chance they could agree.

First Assistant District Attorney Ed McCann Jr. said after the mistrial was declared that he was “somewhat surprised” the jury couldn’t come to a consensus. He said Fisher — who took the witness stand against the advice of his attorney — had ”no reasonable” response to critical pieces of evidence prosecutors presented.

But McCann, who said he will likely again seek a conviction on the same charges, admitted that pursuing the case was a challenge. It was last tried 30 years ago, and some of the key witnesses have died.

Still, he said, “this is an act that happened 41 years ago, and it reverberates today.”

Rowden’s sister, Chris DiDomenico, said her family “will take a hung jury” because it means Fisher will remain incarcerated pending a new trial.

“We are pleased,” she said, “but saddened that this jury could not see the evil in this man.”

» READ MORE: 40 years later, a Montgomery County woman shares her grief as her sister’s alleged killer goes on trial

Prosecutors in Montgomery County allege that Fisher shot Rowden twice as she drove him and another man, Richard Mayo, through Norristown on July 10, 1980. They said she was cooperating with investigators probing the death of another man Fisher was suspected of killing, and surmised he was the only person with a motive to kill her.

Over the years, others have agreed. Fisher has been convicted twice of the killing and sentenced to death three times. But those decisions have been overturned by federal appeals judges who ruled that prosecutorial and judicial errors denied Fisher fair trials.

This time, prosecutors said they would not seek the death penalty if Fisher was convicted.

His attorney, Carrie Allman, cast doubt on the reliability of other witnesses, including Mayo, who told police in 1980 that he watched Fisher shoot Rowden, and testified against him in 1991. But Allman said his story evolved over time, and she theorized he was the killer.

“Why is there no consistent story here?” she said during closing arguments. “If Richard Mayo was in that car, he should have known what happened.”

A status conference to review next steps is scheduled for November.