Police are trying to learn why a 13-year-old boy was shot to death in his bedroom in west Georgia, hours after celebrating his birthday.

Police say witnesses heard gunfire between 1 a.m. and 3 a.m. Sunday. They said relatives later discovered Nizzear Rodriguez with gunshot wounds when they awoke and called 911. Police say relatives were trying to take the boy to a hospital when officers arrived, but he was already dead.

Police originally believed he was killed in a drive-by shooting, but they now believe the suspect went into the boy's room and shot him in the head while in bed, 11Alive.com reported.

WSB-TV reports that Nizzear was an eighth-grader at Carrollton Junior High School. Police say the school planned to have grief counselors on the campus Monday morning. One police officer called Rodriguez an "outstanding kid."

Police charged a 17-year-old with murder. The teens mother convinced him to turn himself into police, 11Alive.com reported. Police are trying to determine if the killing was a result of gang activity in an apartment next door, MyFoxAtlanta.com reported.

Detectives say they are interviewing witnesses and following up on several leads on additional suspects.

Carrollton is about 45 miles west of Atlanta.

The Associated Press contributed to this report