A jury in coastal Brunswick took about two hours to convict 61-year-old David Edenfield in the March 2007 sexual assault and choking death of young Christopher Michael Barrios.
The jury now must decide whether to sentence Edenfield to death or life in prison.
Edenfield is the first of three suspects to stand trial for the boy's slaying. His wife and grown son have also been charged in the crime.
Prosecutors said Edenfield "convicted himself" in a taped confession to police. Defense attorneys said police may have led Edenfield to make a false confession.