The gunman who killed 12 people in a cinema in the US city of Denver has reportedly rigged his appartment to try to kill even more people.
Fifty-eight people were wounded in a shooting rampage - 11 of them are in a critical condition - at a screening of the new Batman film, The Dark Knight Rises on Friday.
Armed with an assault rifle, a shotgun and a pistol, the man hurled a gas canister into the theatre in the Century 16 cinema complex in the suburb of Aurora before opening fire.
The police in Denver have revealed that the suspect, James Eagen Holmes, booby-trapped his apartment and set a timer to go off to turn on very loud dance music that would have eventuated in someone going to the property to complain or take action.
CNN reports that when that person opened the front door or a window that may have triggered explosives which could have brought down the entire building or several buildings.
The authorities evacuated five nearby buildings, and created a perimeter of several blocks as they worked out how to defuse the devices. A police spokesperson says they are unable to enter the apartment and it could be days before they can make it safe.
Police now plan to detonate the devices using a robot.
The police say James Holmes had stockpiled a large array of ammunition before the shooting rampage. When he was arrested he had a rifle, a handgun and a knife, and was wearing extensive body armour. Another gun was found in the cinema.
Aurora police chief Dan Oates says in the past 60 days Mr Holmes purchased four guns at local stores and more than 6000 rounds of ammunition on the internet. The 24-year-old former neuroscience student was arrested in a car park nearby.
Cinemagoers' desperate attempts to escape gunfire
Witnesses described a chaotic scene of bleeding victims, horrified screams and pleas for help. People were crawling down stairs trying to escape the gunfire, one witness said.
Most of the victims are reported to be children or teenagers.
A Denver reporter, Justin Joseph of KDVR, says witnesses told him the man stood up brandishing a gun as soon as Batman appeared on screen. Moviegoers initially thought it was part of the film.
The gunman may have blended in with other filmgoers who wore costumes as heroes and villains, Reuters reports.
New York Police Commissioner Ray Kelly, who had been briefed by Colorado authories, said the arrested man had his hair coloured red and told police he was "the Joker", the fictional Batman opponent.
After James Holmes told police explosives were stored at his home, firefighters, police and sheriff's deputies from several jurisdictions swarmed the scene with heavy weaponry and trucks from the bomb squad.
AFP reports the apartment complex is reserved for students, faculty and staff of the medical school at the University of Colorado. He was a student at the University of Colorado School of Medicine in Denver until he dropped out last month.
US president Barack Obama cancelled presidential election campaign events, saying it was a day for prayer and reflection, not politics.
The shooting evoked memories of the 1999 massacre at Columbine High School in Littleton, also a Denver suburb and 27km from Aurora, where two students opened fire and killed 12 students and a teacher.
The FBI says no terrorism link has been established.
Cinemas in New York tightened security at Batman showings following the attack, and the French premiere of the film in Paris was cancelled, the BBC reports.