Police probing a Colorado shooting rampage prepared on Saturday to send in a robot to detonate what they called a sophisticated booby-trap in the apartment of a man accused of killing 12 people at a screening of the new "Batman" film.
James Eagan Holmes, 24, is accused of storming into a theater in a suburban Denver multiplex just after midnight on Friday clad head-to-toe in black body armor and a gas mask and tossing smoke bombs into the audience before shooting seemingly at random.
The graduate student, who authorities said had dyed his hair red and called himself "The Joker" in a reference to Batman's comic-book nemesis, was taken into custody outside the theater minutes after the attack.
Police later found a set of explosives at his home following his arrest after the shooting at a showing of "The Dark Knight Rises" in Aurora and have been unable to enter.
The massacre stunned Aurora and much of the nation, evoking memories of the 1999 massacre at Columbine High School in Littleton, 17 miles (27 km) from Aurora, where two students opened fire and killed 12 students and a teacher.
It also resonated in the U.S. presidential race as both President Barack Obama and his Republican rival, Mitt Romney, toned down their campaigns, pulled their ads from Colorado and dedicated their scheduled events to the victims on Friday.
Chris Henderson, Aurora's deputy fire chief, said Holmes' living room was found crisscrossed with trip wires connected to what appeared to be plastic bottles containing an unknown liquid.
A law enforcement source told Reuters the suspect had also set a timer to turn on loud music in his apartment - playing the same song over and over again - apparently in an attempt to prompt a complaint and lure police into a trap.
"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," the source said.
Aurora Police Chief Dan Oates said authorities had determined that the apartment was too dangerous for officers to enter and would send a robot in on Saturday to detonate the explosives after consulting with federal authorities.
With Holmes in jail and awaiting an initial court appearance on Monday morning, police have declined to reveal what he has told investigators and would not discuss possible motives for the shooting rampage.
Meanwhile little has surfaced from the suspect's past to suggest he was capable of such violence.
Raised in a middle-class San Diego neighborhood, he earned a degree in neuroscience from the University of California at Riverside before seeking his graduate degree from the University of Colorado.
Holmes was described by acquaintances as bright but was in the process of dropping out of his graduate program at the time of the shooting, according to the university.
Billy Kromka, a pre-med student who worked alongside Holmes in a neuroscience research lab last year, said he was astonished when he saw a picture of the accused gunman.
"He basically was socially awkward but not to the degree that would warrant suspicion of mass murder or any atrocity of this magnitude," Kromka told Reuters in an interview. "I did not see any behavior he exhibited that indicated he would be capable of an atrocity of a magnitude like this."
Kromka, 19, said he knew Holmes to sometimes play video games in the lab when he was supposed to be working and said he seemed to be influenced by movies and the media.
Witnesses at the movie theater told of a horrific scene, with dazed victims bleeding from bullet wounds, spitting up blood and crying for help. Among those taken to hospitals as a precaution was a months-old baby boy.
Confusion reigned as shooting broke out during an action scene in the summer blockbuster. The suspect may have blended in with other moviegoers who wore costumes as heroes and villains, and some witnesses said they believed at first that his appearance was a theatrical enhancement to the film.
The gunman was armed with an AR-15 assault rifle, a 12-gauge shotgun and a Glock .40 caliber handgun, Oates said. Police found an additional Glock .40 caliber handgun in his car, parked just outside the theater's rear emergency exit, Oates said.
He was dressed entirely in black with a gas mask, ballistic helmet, tactical ballistic vest, throat guard, leggings and crotch guard, Oates said, adding that Holmes had purchased the weapons legally at three local gun stores in the last 60 days and had bought 6,000 rounds of ammunition.
Among the dead identified on Friday were Jessica Ghawi, an aspiring sportscaster from Texas who narrowly missed being on the scene of another shooting rampage months earlier in Toronto.
Family members of 27-year-old Alex Sullivan told local NBC affiliate, 9NEWS, that he was among those killed. The Los Angeles Times reported that 23-year-old Micayla Medek also died in the attack, citing family members.