The official spoke on condition of anonymity because of the sensitivity of the investigation into an incident that has roiled relations with Afghanistan.
American officials had previously said the suspect was a 38-year staff sergeant and that he had spent 11 years in the Army. But they had refused to release his name, saying it is military policy to publicly name a suspect only after he has been charged with an offense.
Bales has not yet been charged. He was being flown Friday from Kuwait to a military detention center at Fort Leavenworth, Kan.