Last Haloween, notorious drug-dealer-and-murderer-turned snitch Alpo Martinez was shot to death in his hometown of Harlem.

The 55-year-old was hit on West 151st Street in Manhattan while he was in his Dodge Ram.  The SUV drove four blocks and crashed on 147th street.  Alpo died on the way to the hospital.

Police have now arrested Shakeem Parker for the killing.  

The 27-year-old, who lived on 149th street in Harlem, was already in custody on Rikers Island for a previous gun case.

He's been charged with murder and criminal possession of a weapon.

“Detectives gathered information that he was the shooter,” a police spokesman said.

Parker has a long list of priors.

In 1990, Alpo confessed to 14 murders, including the killing of his boyhood friend Rich Porter.  He got 35 years in exchange for helping the government.  He was released into witness protection in 2015 and moved to Maine. But he had been increasingly seen around Harlem and there was speculation he was back in the drug trade.