The discovery was made inside a home on 2400 Seventh Ave near West 140th Street over the weekend.
An autopsy determined the woman sustained wounds to the torso, injuring her major organs. The cause of death was ruled a homicide.
Officials are still working to make a positive identification of the body, which they say had been in the barrel for several days and was decomposing.
A young man who lives in the room where the body was found is in police custody and undergoing a psychological exam at St. Luke's Hospital.
Detectives plan to question him about the death, which is preliminarily being investigated as a domestic dispute.
The body was found after the man's grandmother called police about a foul odor coming from the room Saturday night.