The suspect who allegedly stabbed a teenager he smiled menacingly at is an ex-New York inmate with 15 previous arrests

An ex-convict with 15 previous arrests was arrested for randomly stabbing a teenager in the neck near City Hall and then flashing a menacing smile at the victim, cops said Thursday.

Smiling maniac Marvin Dupree, 41, allegedly walked up behind Brooklyn College student Alan Ryvkin and stabbed him in the neck around 11:30 a.m. as the 19-year-old waited outside a Center Street building to contest a vehicle summons , according to authorities .

Police caught up with the smiling alleged killer in Harlem hours after the attack and charged him with felonious assault, authorities said.

Ryvkin said he was talking to a woman outside the building at 1 Center St. when the stranger silently walked up behind him and stabbed him.

“When he walked away, the guy looked at me and smiled with the knife in his hand,” Ryvkin exclusively told the Post over the phone on Wednesday.

“I didn’t know who it was. I don’t know what it is. I was stabbed and I sat on the floor and started bleeding.”

Sam Townsell, 24, a bartender at the outdoor bar Jury Duty, watched as Ryvkin, bloodied and apparently in shock, was loaded into an ambulance.

She said she was shocked when the late-morning violence unfolded just steps from NYPD headquarters.

“It’s scary — there’s a police department right there,” Townsell said.

“You wouldn’t think that acts of violence like this would happen in an area like this, where there are police everywhere. There’s no place around here where you wouldn’t see a police officer, so it’s kind of scary.”

Doctors rushed Ryvkin to Bellevue Hospital, where they treated him for a stab wound between his lower neck and upper back.

“It’s horrible,” said the longtime New Yorker. “It seems like New York is not the place to be. It’s very unsafe.”

Meanwhile, Dupree was also taken to Bellevue following his arrest for unknown reasons, deputies said.

Dupree’s criminal record includes arrests for assault, aggravated harassment, criminal possession of a controlled substance, menacing and resisting arrest, deputies said.

His most recent arrest was in July for menacing in Harlem, but the case has since been closed, police said.

His last assault was in June 2012, also in Harlem, but the case was also closed, according to authorities.

He was previously convicted of criminal sale of a controlled substance and served just over four years in state prison before being paroled in November 2019, records show.

He previously served a six-year sentence for drug sales before being paroled in October 2013, and spent less than a year in prison for drug possession until he was paroled in July 2006, according to records.