A man who fatally shot a 21-year-old overnight in the driveway of a Cobb County home said he acted in self-defense, police said Tuesday.

The shooting happened shortly before 2 a.m. outside a home in the 1200 block of West Sandtown Road near Marietta, Cobb police spokesman Sgt. Wayne Delk said in an emailed statement. Officers arrived at the scene and discovered Christopher Hunter Tillman with two gunshot wounds.

He was rushed to Wellstar Kennestone Hospital, but died of his injuries.

“Witnesses at the scene provided information which indicated Tillman physically assaulted another male at the residence who then used a firearm to defend himself,” Delk said.

The shooter, who was not identified, is cooperating with investigators, authorities said. It’s unclear if the two men knew each other.

The case remains under investigation. Anyone with information is asked to call Cobb police at 770-499-3945.