When Paul Fritze was 23 years old, he commandeered a New Jersey public bus at gunpoint.

Fritze was late for work and couldn’t find his car keys, said his sister, Zina Fritze. He spent a year in a mental institution undergoing evaluation before he was transferred to federal prison to serve a five-year sentence for kidnapping and robbery, she said.

It was an early example of how Fritze’s social disorders and impulsivity could led to harsh consequences. Adding alcohol and drugs to the mix made for a fatal combination.

Fritze, 41, was shot and killed by police in Farmingdale on Sept. 24, 2011, after he allegedly terrorized a couple in their home with a 9mm semiautomatic pistol.

According to the Maine Attorney General’s Office, which reviews all police shootings, the Maine State Police officer who shot Fritze was justified because he reasonably thought Fritze might shoot another member of the police tactical team.

A separate, critical incident review by the state police found no deficiencies in how the matter was handled and noted that nobody else was harmed in the confrontation.

Fritze was born in New Jersey and while growing up, his family enjoyed vacationing in Maine in the summer. When he and his younger brother were in middle school, their parents gave up city life to buy a farmhouse in Richmond on a dozen acres where their mother grew produce, Zina Fritze said.

Paul Fritze attended Richmond High School, but as a teenager he was already showing signs of trouble, getting kicked out of school at one point, said Zina Fritze, who is 18 years younger than Paul and learned about his young life from her family.

“He wasn’t very socially equipped,” she said. Her brother had obsessive compulsive disorder and was diagnosed with Asperger’s Syndrome, a form of autism, she said.

It was his inability to find his car keys that triggered his irrational behavior in New Jersey, she said. The way she heard the story, when the bus driver dropped him off a couple blocks from work, Fritze tipped him and apologized for the inconvenience.

He was released from prison in 1999, but his freedom didn’t last. He was caught with a gun, a felony because he had a record, and was sent back to prison.

When he returned, his sister barely recognized him.

“He didn’t look like my brother,” she said. “He had gained some weight, had a big beard where he was usually clean-shaven. He looked like the man from the mountains.” He also had been taking heavy doses of anti-psychotic medication.

Paul Fritze moved into a house in Farmingdale, sharing it with his uncle. He tried to work at some fast-food restaurants, but his lack of social tact made that impossible, his sister said, so he subsisted on disability checks.

His uncle committed suicide, and Fritze became estranged from his father.

“He was always kind of obnoxious when he got drunk, but he was very angry. He just wasn’t himself. He was drinking a lot more,” his sister said.

The day before his death, Fritze visited a neighbor and asked for help with his drinking. He told her, “You’re looking at a dead man. … I’m a dead man walking,” according to investigators.

Fritze’s medical history included depression, anxiety disorder, agoraphobia – a fear of open spaces or uncontrolled social situations – obsessive compulsive disorder and personality disorder with schizoid traits, according to an investigation after the shooting.

He had been drinking heavily on the day he was shot. Fritze had texted his neighbor, asking if he wanted to play cards as they often did. When the neighbor declined, Fritze walked to the house and confronted him in the yard. He pointed a gun at his head and ordered him inside.

The man and a woman who was also in the house eventually escaped.

The state police tactical team surrounded the house, and a negotiator tried to contact Fritze. He told the officers he didn’t have a telephone.

Four hours after he arrived at the house, Fritze walked out onto a porch and pointed a black semi-automatic handgun at a nearby tactical team vehicle.

“If you want a gun battle, here,” he said, according to the investigators’ report.

Trooper Timothy Black, a tactical team sniper, killed Fritze with a single shot.