Law enforcement officials say a 5.7-millimeter pistol used in the Fort Hood shooting rampage was purchased legally at a Texas gun store.
The officials spoke on condition of anonymity because they were not authorized to discuss the case.
Records indicate Hasan bought the FN 5.7 at store called "Guns Galore" in Killeen, Texas, well before the attack that left 13 people dead. The pistol has been dubbed a "cop killer" by those who have tried to stop its use.
The most powerful type of ammunition for the gun is available only to law enforcement and military personnel. Gun control advocates call it a "cop killer" weapon because that ammo can pierce bulletproof vests, and its use by Mexican drug cartels worries police.