AURORA, Colorado - Police on Saturday prepared to enter an apartment rigged with explosives that belongs to the man believed to have opened fire at an opening of the latest Batman movie, killing 12 moviegoers.
Bomb squad experts have been scoping out the apartment since shortly after the suspect, 24-year-old James Holmes, allegedly entered a packed cinema early Friday showing the "The Dark Knight Rises" and opened fire.
Twelve people were killed by the hail of gunshots and 58 others wounded.
There may be a controlled detonation when bomb squad experts finally enter Holmes's third-floor apartment, said Sergeant Cassidee Carlson with the Aurora Police Department.
Carlson said experts will first focus on rendering inactive a trip wire that has thwarted operations up to now.
"This may also include a controlled detonation," Carlson told reporters. "That may cause a loud boom and there may also be a fire that erupts at that point."
The bomb squad is coordinating closely with fire department personnel, who will be prepared to douse any flames, she said.
Experts will then take some 30 high-power fireworks they have identified and remove them in sand containers.
Carlson said experts need to be careful to save as much material as possible for evidence. "We don't need to rush anything," she said, adding that "national experts" on explosives and chemicals have flown in to help the local bomb squad.
"There are still unknowns," Carlson cautioned. "We're not exactly sure of everything that's in there."
Aurora police chief Dan Oates earlier described the apartment, which he saw via footage taken by a robot: "I see an awful lot of wires, trip wires, jars full of ammunition, jars full of liquid. Some things that look like mortar rounds."
The shooting drew expressions of concern from political leaders led by President Barack Obama, and revived the national debate about gun control.
"The federal government stands ready to do everything necessary to bring whoever's responsible for this heinous crime to justice," Obama said Saturday.
Late Friday the town near Denver gathered for two vigils as it emerged that Holmes bought more than 6,000 rounds of ammunition on the Internet, and four guns, in the two months before the rampage.
Hundreds of mourners held candles at the event, many sobbing and hugging each other in an outpouring of grief for those who died in the rampage.
The shooter, dressed in black and wearing body armor and a gas mask, burst into the movie theater barely 20 minutes into the midnight screening early Friday, throwing two tear-gas type devices before opening fire.
A local children's hospital reported six young victims, the youngest of whom was aged only six. At least three of the wounded were US military members, the Pentagon said.
Shots fired in one auditorium went through the wall and hit people in the auditorium next door. The first police officers were on the scene within 90 seconds, while eventually some 200 swarmed around the building.
Police arrested Holmes by his car at the rear of the theater. He offered no resistance.
According to Oates, "all the weapons that he possessed he possessed legally, and all the clips that he possessed, he possessed legally, and all the ammunition he possessed, he possessed legally."
Holmes, who attended the University of Colorado medical school until last month, had no criminal record aside from a citation for speeding in October 2011, according to police.
Witnesses described chaos chillingly similar to that depicted in the Batman films, in which maniacal villains terrorize Gotham City.
"I saw some people start to get up. I poked my head up to see what was going on and when I did that I saw another flash and instantly put my head down as he started shooting again," said 17-year-old Tanner Coon.
Cinemas in New York tightened security at Batman showings, and the AMC theater chain announced a ban on face masks and fake weapons -- several people wore costumes in Aurora, possibly helping Holmes to blend in with the melee.
The French premiere of the film in Paris was canceled.
As with previous such shootings, lobby groups and some political leaders called for legislation to restrict civilians' access to firearms.
Aurora is 20 miles (32 kilometers) from the scene of the 1999 Columbine High School massacre, in which two students shot dead 13 people before committing suicide.
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