Rapper Proof fired the first bullet in a Detroit nightclub shootout that ended his life, police said Wednesday.

The bullet hit Keith Bender, 35, in the head, critically injuring him early Tuesday at the C.C.C., a bar in a strip of businesses along Eight Mile, the road made famous in Eminem's movie of the same name.

Proof, whose real name is Deshaun Holton, was taken to a nearby outpatient treatment center by a private car, where he was pronounced dead.

Detectives are currently trying to figure out who shot Proof, said Detroit police spokesman Sgt. Omar Feliciano. He said his office was told by homicide detectives that Proof fired the first shot at Bender.

Feliciano said no further information has been released.

Proof, 32, was a member of the rap group D12 and was the best man in Eminem's January wedding. Eminem was seldom seen in public without Proof.

Police said officers responding to 911 calls about 4:30 a.m. Tuesday found the bar empty when they arrived.

Bender also was taken to a hospital by a private car.

Police Chief Ella Bully-Cummings said Tuesday that detectives don't know what Proof was doing at the bar, which was operating outside of its licensed hours. Investigators face a unique challenge because no victims were present at the crime scene, Bully-Cummings said.

Police have said that an argument between two parties at the club escalated into gunfire.