A man has been arrested for fatally shooting his mother’s boyfriend in the head in Harlem, police said Monday.

Tomas Dunn, 22, turned himself in to cops Sunday, nearly three weeks after the deadly shooting at the Frederick Samuel Apartments on West 144th Street in Manhattan.

Dunn faces counts of murder and criminal possession of a weapon in connection with the Sept. 30 shooting of 41-year-old Saladeen Cochrane, authorities said.

Cochrane, who had been dating Dunn’s mother, was found unresponsive in front of 112 W. 144th St. with a gunshot wound to the head just after 10 p.m., the NYPD stated.

He was transported to NYC Health & Hospitals/Harlem, where he died three days later.

It’s unclear what sparked the shooting.

Cochrane was said to have had a lengthy rap sheet dating back 25 years, which included multiple drug convictions.