The suspect in the deadly shootings in Colorado had an assault rifle, a shotgun and two pistols.
A federal law enforcement official said the suspect, identified by other federal law enforcement officials as James Holmes, also used a gas canister in the attack in a movie theater in the Denver suburb of Aurora, Colo. The official spoke on the condition of anonymity to discuss the ongoing investigation.
Officials believe Holmes, who was wearing a gas mask during the attack, killed a dozen people when he open fired in the crowded theater.
Investigators from the Bureau of Alcohol, Tobacco, Firearms and Explosives, along with other local, state and federal law enforcement officials, are investigating the overnight attack.