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Police are searching for an unidentified suspect in the murder of a social justice activist who was stabbed multiple times on a New York street while returning from a wedding.

Ryan Carson, 32, was murdered near a bus station in Brooklyn's Crown Heights neighbourhood early on 2 October.

The suspect, who has not been named, was "acting agitated" before the unprovoked assault.

Mayor Eric Adams vowed that police "won't rest" until an arrest is made.

Surveillance camera footage shows the suspect, dressed in dark clothing, Mr Carson and an unidentified woman at a bench near a bus stop at about 04:00 local time (08:00 GMT).

According to officials, Mr Carson and his companion began to walk away after seeing the suspect kicking over parked scooters before he confronted them and began shouting obscenities.

"Mr Carson then immediately places himself between the man and his female companion to protect her," NYPD Chief of Detectives Joseph Kenny told reporters on Wednesday, adding that Carson was attempting to "de-escalate" the situation.

Soon after, the suspect stabbed Mr Carson three times, including one blow to the chest that pierced his heart and ultimately killed him.

"As Mr Carson lay dying on the sidewalk, the male with the knife kicks him in the chest, threatens to stab the woman companion and spits in her face," Mr Kenny added.

An unidentified woman, believed to be the suspect's girlfriend, arrived soon after and apologised.

On Wednesday, police released an image of the suspect and his girlfriend and sought the .

According to local media, police are withholding the identity of the suspect - an 18-year-old with a history of disorderly conduct - until authorities have enough probable cause to make an arrest.

Mr Carson had lived in New York for 13 years. For a decade, he helped organise campaigns for the New York Public Interest Research Group, which is focused on waste policy.

Additionally, Mr Carson helped create a campaign called "No OD NY", which was aimed at raising awareness of overdose prevention centres.

In 2021, he walked over 150 miles from New York City to Albany to raise awareness of the centres and other harm reduction measures, .

"He advocated tirelessly for others, and his giving spirit was a buoy to all," New York Mayor Eric Adams wrote on X, the platform formerly known as Twitter. "His murder is unthinkable and the NYPD won't rest until we bring him justice."

Senator Chuck Schumer, who worked with Mr Carson at a town hall regarding inflation, called him a "rising talent and extraordinary activist".

"May his memory and work inspire us," the Senator wrote on X.