Detectives have arrested an 18-year-old man they say played a role in the murder of a 42-year-old man shot in the neck at a Harlem smoke shop in February, police said Saturday.

After nearly four months on the run, police apprehended suspect Christian Marte on Thursday, cops said.

He is accused of taking part in the murder of Alfred Johnson, 42, who was in the neck and torso during a spat inside Level Up Exotics, a smoke shop with a “Super Mario Bros.”-themed awning on W. 125th St. near Fifth Ave. about 10:05 p.m. on Feb. 11, cops said.

Medics took Johnson to Harlem Hospital, but he couldn’t be saved.

A blood trail was still visible outside a Shake Shack restaurant across the street from the smoke shop.

Members of the NYPD Warrants Squad grabbed Marte in Harlem after he had been identified as one of the men inside the smoke shop at the time of the killing.

A few days after the slaying, cops released surveillance images of one of the men, believed to be Marte, at the scene and asked the public for help identifying him.

Cops initially charged Marte with murder as well as gun and drug possession, although Manhattan prosecutors dropped the murder charge as they collected more evidence and continued to investigate.

Marte was arraigned on Friday and ordered held on $100,000 bail, according to court documents.

At least one other suspect was being sought in the killing, police said.

Marte lives in Washington Heights, about a mile from the smoke shop where the killing took place.

Johnson also lived in Washington Heights, about three blocks from Marte, although it was not immediately clear if the two men knew each other.

A motive for the killing was not immediately disclosed.

The smoke shop bloodshed came on the heels of a rash of shootings citywide during a frightening 15-hour span that saw 14 people wounded — three fatally. Five people were blasted in the Bronx, five in Brooklyn, and four in Queens in eight separate incidents between 2:30 p.m. on Feb. 10 and 5 a.m. on Feb. 11.