Bomb disposal experts are preparing to send a robot to detonate a sophisticated booby-trap in the apartment of James Holmes, the accused in the Aurora, Colorado, shooting.
The police could not access the dwelling on Friday as they believed that explosives had been primed to explode on entry.
Holmes' living room was found to be crisscrossed with trip wires connected to what appeared to be plastic bottles containing an unknown liquid, Chris Henderson, Aurora's deputy fire chief, told Reuters.
"I've personally never seen anything like what we've found in there," said Aurora police chief Dan Oates.
According to the police, Holmes even set a timer to play loud music on a loop, in an apparent attempt to encourage neighbours to complain, thereby luring police into the house.
"If he was shot and killed, it is without a doubt that these ... booby traps were there to murder and inflict casualties upon first responders," a police source told Reuters.
Holmes was armed with an AR-15 assault rifle, a 12-gauge shotgun and a Glock .40 calibre handgun. Police found an additional Glock .40 calibre handgun in his car, parked just outside the cinema's rear emergency exit, Reuters reported.
According to the police, the accused had made online purchases of 6,000 rounds of ammunition in the past 60 days.
Twelve people were killed and at least 50 injured in the shooting. Holmes stormed into the cinema dressed in black armour and wearing a gas mask.
He released a gas canister into the audience and started shooting people at point blank range. At first, the audience thought it was part of a promotional stunt.
Meanwhile, a candle-lit vigil has taken place in Aurora, where hundreds of people have gathered to say prayers for the victims.