The official, speaking on condition of anonymity because they were not authorized to discuss the case, says James von Brunn died at a federal complex in Butner, North Carolina.
Von Brunn had been awaiting trial for the killing of security guard Stephen T. Johns at the U.S. Holocaust Memorial Museum on June 10. Von Brunn had been wounded by return fire but survived.
Officials at the prison hospital had previously said chronic medical problems had complicated a psychiatric evaluation for the suspect, a white supremacist who prior to the shooting had written racist and anti-Semitic screeds on the Internet.