ASTORIA – Peter Zisopoulos was known as a loner who walked the streets of his Astoria neighborhood in a kind of troubled shuffle, not talking to anyone, one of the kind of odd fixtures that people get used to but eye warily.

Now he has been held in the savage, sudden, senseless killing of a decorated paramedic, Lt. Alison Russo-Elling, 61, jumped on a street corner on the way back to work from lunch and stabbed more than 20 times in seconds.

It was shocking even in a New York City almost inured to growing violence on the subway and streets, chilling reminders of the dark metropolis it was in the 1970’s, but this attack stopping people in their tracks in fright.

The New York Times wrote of the circumstances that led to Zisopoulos, 34, who lived with his parents and sisters, being caught on a surveillance camera during the murder and later taken into custody at their home after he barricaded himself inside.

The video from a nearby business was so graphic and disturbing that CBS News said it wouldn’t show it and neighbors told the station they frequently saw Zisopoulos wandering aimlessly and that he seemed “unhinged.”

The camera also showed a man on a motorbike noticing the 2:15 p.m. attack on Sept. 29, slowing before the suspect caught on film chased him with the knife before turning around and walking calmly past the victim without looking at her and she lay motionless.

Peppy Oomraw, the owner of an auto repair shop up the block from the attack, said he watched as the man stabbed Lieutenant Russo-Elling.

“I saw her on the floor, I knew I couldn’t help her,” Oomraw said. “It did not look good.” He said he chased the attacker and followed him to the apartment building, watching him run upstairs before police arrived.

The paper said that shopkeepers, residents, deli workers, mechanics and others interviewed described Zisopoulos walking up and down the block every day, ignoring everyone, thinking him peculiar but harmless.

“We try to be friendly, but he always seemed very out of it,” Brennan Rogan, 23, a manager nearby at Kate’s Corner Cafe told the paper, and no one, it seemed, thought he could be dangerous.

“He never had a specific destination — he would just walk,” said Rogan. “All hours of the day. All seasons. He was a loner, isolated.”

“He never speaks,” said Miguel Tenecela, the superintendent of  Zisopoulos’ building. “I see him in the street, in the hallway. He never is speaking. Sometimes I say ‘Hi.’ He says nothing.”

The report said the police responded to a call to Zisopoulos’s home four years ago, and his mother told officers her son took medication for schizophrenia, a senior law enforcement official not named said.

Russo-Elling, a 24-year veteran, dedicated her life to her service and was a first responder at the Sept. 11, 2001 terrorist attacks that felled the Twin Towers of the World Trade Center. She was a grandmother looking toward retirement.

“She loved being a paramedic,” said Deputy Chief Gregg Brady. “She was there for me when I was at my most vulnerable — she put her arm around me and said ‘Everything is going to be OK.’ Unfortunately, I didn’t have that capability (when she was attacked).’”

Police said that Zisopoulos did not have an arrest record. Officers responded to a call to his apartment in 2018 that led to him being taken to a hospital for observation after he sent a disturbing text to a friend, a source told the paper. He was charged with murder and criminal possession of a weapon.