An 87-year-old, transgendered New York City serial killer is trying to stay out of prison for a third time, as his trial for viciously butchering a woman and then riding around with her severed arm in his mobility scooter began this week in Brooklyn.

Harvey Marcelin stands accused of gruesomely slaying 68-year-old Susan Leyden and chopping up her body into pieces, which he stuffed in a bag and dumped on an East New York street before taking his disturbing scooter ride in March 2022.

Marcelin sat in a wheelchair, dressed in a black jacket, pants, and a white shirt, as a jury was told how he allegedly became so obsessed with his victim that he created multiple Facebook accounts using her photo as his profile picture, the NY Daily News reported.

“On Feb.27, 2022, Susan Leyden went over to the defendant’s apartment at 50 Pennsylvania Ave., carrying her grey and black rolling bag with her, there to see her friend,” Assistant D.A. Viviane Dussek told the jury during her opening argument Monday.

“Susan Leyden walked into that building not knowing she would never walk out again,” she added.

Marcelin, who asked to be referred to as “Mr. Harvey” in court even though he has previously identified as transgender, allegedly bludgeoned Leyden to death and used a reciprocal saw to dismember her body at his Cypress Hills apartment, according to prosecutors.

“Cutting through skin, cutting through flesh, through tissue, through bones. So many bones. So many cuts. He packages Susan’s body up in plastic bags,” Dussek said.

Leyden had been down on her luck at the time after losing her jewelry business, becoming estranged from her daughter, and ending up in a homeless shelter, but had “started getting back on track” just before the murder, Dussek said.

Prosecutors allege Marcelin disposed of Leyden’s torso in the same rolling bag she brought over, before heading to a 99-cent store with part of her left leg stuffed into his electric wheelchair.

After e-bike rider Ramon Lopez discovered Leyden’s torso near the corner of Pennsylvania Ave. and Atlantic Ave. and alerted the police, the NYPD reviewed video of the scene and determined that Marcelin had left the bag.

Inside his apartment, they found Leyden’s thighs, hand, arm and head, stuffed into black plastic garbage bags.

The victim’s right leg, left arm and left hand were never recovered, Dussek said.

Marcelin served time for fatally shooting his girlfriend, Jacquieline Bonds, in the hallway of a Harlem apartment building.

On Oct. 30, 1985, he stabbed another girlfriend, Anna Laura Serrera Miranda, to death in their apartment, a year after being released on lifetime parole for Bonds’s murder.

He brought her body down in a bloody garbage bag before shoving it into a shopping cart.

In 2019, Marcelin was released on parole after vowing to keep his nose clean.

“I give you my word, I will never reoffend,” he told the parole hearing on June 25, 2019, less than three years before he would kill again.

However, prosecutors will only be allowed to bring up Miranda’s murder if Marcelin takes the stand in his own defense, after a ruling from Judge Danny Chun last week.

The jury will not be able to hear any details from the Bonds murder, after Judge Chun ruled that it had happened so long ago that it would only serve to prejudice the jury against Marcelin.

Marcelin has maintained his innocence throughout the case.

His lawyer has suggested that another woman, homeless drug addict Lisa Lindahl, could be responsible for the killing.

Lindahl, who had visited Marcelin on the day of the murder to do drugs with him, reportedly walking in on the horrific crime scene.

“She lied, she was desperate, and now instead of being charged with murder, Lisa Lindahl is the prosecution’s star witness against Mr. Harvey,” defense lawyer Alison Stocking told the jury.