The suspect made the claim of being the fictional archenemy of Batman during the investigation of the shooting early Friday in a movie theatre showing "The Dark Knight Rises", CNN said citing a federal law enforcement source.
At least 12 people were killed and 58 were injured, one fewer than earlier reported, in the rampage at the midnight premiere of the movie in Aurora, about 16 km from downtown Denver in Colorado state.
Families of the victims mourn the loss of their loved ones after shooter goes on a rampage in Denver killing several at movie premiere. Photo: AFP
Pentagon officials have confirmed at least one sailor and two airmen were among the injured in the shooting. They also confirmed that the alleged gunman in this incident, James Holmes, is not a past or current member of any branch or component of the US armed forces.
Of those injured "nearly everyone was shot," Aurora Police Chief Dan Oates said Friday night, adding that a handful of people were hurt in the resulting chaos.
Ten of the victims were killed inside the theatre while two others died at hospitals. As of Friday evening, the 10 bodies had been removed from the complex and authorities were preparing to begin "the agonizing process" of notifying families, Oates was quoted as saying.
Oates declined to comment on Holmes' appearance other than to describe what he was wearing, and said he would not release his booking photo "for investigative reasons."
Police say Holmes, 24, dressed head-to-toe in protective tactical gear, set off two devices of some kind before spraying the Century 16 theatre with bullets from an AR-15 rifle, a 12-gauge shotgun and at least one of two .40-caliber handguns police recovered at the scene.
Oates said the guns were purchased legally by Holmes at stores in the Denver area in the past two months. More than 6,000 rounds of ammunition were also purchased online, according to Oates.
Calling for the country to unite as one and support the victims, President Barack Obama cancelled campaign events Friday, telling supporters in Fort Myers, Florida, that "there will be other days for politics."
"This will be a day for prayer and reflection," he said. Flags at the White House were lowered to half-mast Friday afternoon in honour of the victims.
Christopher Nolan, director of "The Dark Knight Rises," condemned the shooting as "savage" and "appalling."