Police said they are searching for an 18-year-old male suspect in the apparently random fatal stabbing of a New York City social justice advocate.

Ryan Carson, 31, died after being stabbed in the chest multiple times during an assault early Monday morning in Brooklyn, police said.

The suspect in his murder works at a school in the Clinton Hill neighborhood of Brooklyn, police said Wednesday. Authorities are searching for him in the area and other locations he is known to frequent.

The NYPD released a photo Tuesday of the unidentified suspect. Police are working to develop probable cause to make an arrest, NYPD Chief of Detectives Joseph Kenny told reporters during a press briefing Wednesday.

The suspect is said to have had prior summonses for disorderly conduct in 2022.

The apparently unprovoked attack occurred shortly before 4 a.m. Monday. The incident was captured on surveillance footage.

The suspect walked past the couple while they were seated on a bench at a bus stop, police said. As the two then walked toward the suspect, he started to damage scooters and said to Carson, "What are you looking at?" according to Kenny.

As Carson tried to de-escalate the situation, the suspect swung a knife at him, Kenny said. Carson backed up and tripped, falling to the ground. The suspect then stabbed him three times, with the knife piercing his heart, Kenny said.

Prior to the attack, the suspect was seen "acting agitated" while talking to a woman police believe to have been his girlfriend, Kenny said. Following the stabbing, the woman apologized to the couple and said the name Brian, Kenny said.

First responders attempted lifesaving measures before transporting Carson to a local hospital, where he was pronounced dead, police said.

Carson and his girlfriend were coming home from a wedding at the time of the attack, New York ABC station WABC reported.

He was a longtime campaign organizer for the New York Public Interest Research Group, a non-partisan political organization, focusing on waste policy. He also created the campaign No OD NY, which raised awareness for overdose prevention centers.

NYC Mayor Eric Adams called his murder "unthinkable," and vowed that the NYPD "won't rest until we bring him to justice."

"He advocated tirelessly for others, and his giving spirit was a buoy to all," Adams said on social media Tuesday. "I'm praying for all who knew and loved Ryan."