Washington: The US police on Saturday struggled to establish motive behind the deadly shooting spree at a cinema hall and explored ways to collect possible evidence from the suspect`s "booby-trapped" house, as President Barack Obama vowed to bring to justice whoever was behind the "evil" act.
A day after the shooting, which claimed 12 lives and left 58 people injured, it remained unclear what was the motive of the gunman, identified as 24-year-old James Holmes, to fire indiscriminately at the moviegoers during the premiere of the latest Batman film `The Dark Knight Rises` in Aurora, a suburb of Denver, Colorado.
As police began the process of notifying the families of those killed, authorities grappled with how to collect possible evidence from Holmes` apartment that was allegedly booby-trapped by him before leaving for the theatre.
Police evacuated hundreds of residents from five apartment buildings, including the one where Holmes lived, after he told them he had rigged his one-bedroom apartment with explosives.
"It is a very vexing problem how to enter that apartment safely. I personally have never seen anything like what the pictures show us is in there," city police chief Dan Oates was quoted by CNN as saying.
A vigil was organised to mourn the death of innocent victims as hundreds held candles, many sobbing and hugging each other in an outpouring of grief.
Ten people were killed inside the theatre while two others died at hospitals. By last night, the bodies were removed from the theatre and authorities started "the agonising process" of notifying families, Oates said.
Of those injured, "nearly everyone was shot," with only a handful of people hurt in the resulting chaos, Oates said.
Describing the shooting as an "evil" act which was "beyond reason”, President Obama today said his government "stands ready to do everything necessary to bring whoever`s responsible for this heinous crime to justice”.
In his weekly radio and Internet address, Obama pledged that his administration "will take every step possible" to ensure the safety of all the residents of the country.
Witnesses to the shooting said the gunman was wearing a gas mask that concealed much of his face and head.
Oates declined to release details about Holmes` appearance other than to describe what he was wearing, and said he would not release his booking photo "for investigative reasons”.
He said the man was wearing a ballistic helmet and protective gear for his legs, throat and groin, black gloves and a gas mask.
The shooting unfolded inside the darkened theatre packed with Batman fans, some in costume for the premiere of the movie.
Screaming, panicked moviegoers scrambled to escape from the black-clad gunman, who shot at random as he walked up the theatre`s steps, witnesses said.
Police said Holmes set off two devices of some kind before spraying the 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.
Holmes bought the guns legally at stores in the Denver area over the past two months, Oates said.
More than 6,000 rounds of ammunition were also purchased online, according to Oates.
The Defence Department released a statement saying one sailor was injured and another one, known to have been at the theatre, was unaccounted for. Two airmen were wounded in the incident, it said.
As of yesterday, 30 people remained hospitalised, 11 of them in critical condition, Colorado Governor John Hickenlooper said.
Holmes is scheduled to appear in an Arapahoe County, Colorado, courtroom on Monday morning, said Rob McCallum, a spokesman for the Colorado Judicial Department.
The court file was sealed, according to a court order. He is being held in the Arapahoe County jail, Oates said.
Batman movie director Christopher Nolan has lamented the "senseless tragedy` and "unbearably savage".