Police said they are seeking a suspect in the murder of a man who was stabbed multiple times near a bus stop in New York City early Monday in an "unthinkable" attack.

The incident occurred in Brooklyn shortly before 4 a.m., according to police. Ryan Carson, 32, a well-known social justice advocate, died after being stabbed in the chest, police said.

Carson and his girlfriend were coming home from a wedding when the apparently unprovoked attack occurred, ABC New York station WABC reported.

The NYPD released a photo Tuesday of an unidentified male suspect being sought in the murder. No arrests have been made at this time, a police spokesperson said Tuesday night.

Carson 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 on Tuesday. "I'm praying for all who knew and loved Ryan."

Carson started working for NYPIRG while a student at Pratt Institute, the organization said.

"Ryan was a beloved staffer, colleague and friend, and a creative, talented, relentless and upbeat advocate for students and the environment," NYPIRG said in a statement. "His engaging personality, hearty laugh and wide-ranging intelligence were keys to his success in advancing the causes he deeply cared about in his work and personal life.

He was remembered as a passionate social justice advocate by friends, colleagues and New York politicians, who expressed shock at his death.

"It's incredibly tragic," NYPIRG executive director Blair Horner told WABC. " A life full of promise is snuffed out. And the world is a worse place for it."

Senate Majority Leader Chuck Schumer, D-N.Y., said Carson was a "rising talent and an extraordinary activist."

"Ryan Carson threw himself into everything he did with passion and humanity," Schumer said on social media on Tuesday. "May his memory and work inspire us."

New York state Sen. Julia Salazar responded to the "shocking, horrific" news of his death.

"I learned a lot from Ryan in a short time," she said on social media on Tuesday. "I'm better for having known him, as so many of us are. Let us dedicate ourselves to continuing his life's work, cut short far too soon: to harm reduction; to humane drug policy; to creating a more caring society for all of us."

New York State Assemblymember Emily Gallagher remembered Carson as an "accomplished poet" and "deep, sensitive thinker" who was devoted to environmental advocacy.

"Ryan was the kindest, funniest, and hardest working man in advocacy," Gallagher said on social media on Monday. "He and I bonded because our friends died in the opioid epidemic, & we struggled to make good out of our grief. He put his whole heart into making the world a safer place for all people."