| AURORA, Colo.
AURORA, Colo. The sophisticated booby-trap devices Denver-area shooting suspect James Holmes set at his apartment could have killed first responders and destroyed the apartment complex in a massive inferno, an official involved in the probe said on Saturday.
Bomb experts entered the 800-square-foot apartment in the Denver suburb of Aurora after a controlled explosion on Saturday. Inside they found 30 aerial shells filled with gunpowder, two containers brimming with liquid accelerants and an unknown number of bullets left to explode in the resulting fire, according to a law enforcement official on the scene with expertise in improvised explosives.
"Given the amount of explosives that were there, if they detonated ideally, you would have had a very ample explosion with an ensuing thermal effect from the incendiary liquids that would have destroyed that apartment complex," the official, who spoke on condition of anonymity, said.
"It's safe to say that whole building would have burned. The explosion would have certainly removed the interior walls in the building and some of the exterior walls" of the brick-built apartment complex, the source added.
Graduate school dropout Holmes, 24, is in police custody and accused of killing 12 and injuring 58 people at a Denver-area movie theater.
Police suspect he left a stereo device on a timer in his apartment that blared loud music into the early hours, to lure first responders to the carefully rigged home.
The gunpowder filled aerial shells - compared in some accounts to mortars used at public firework displays - were spread throughout the living room area. The shells were wired to an improvised control box in the kitchen.
Designed to be triggered by entry to the apartment, the ensuing blast, conflagration and flying shrapnel from exploding bullets, was clearly designed to kill first responders at the scene.
"There's no doubt in our minds that the trap that was set was purposeful, to kill, murder and maim any first responders, be it through fire or explosion," the source said.
Construction of the potentially lethal booby trap showed a rarely seen degree of sophistication for an improvised bomb made in the United States, where amateur efforts rarely move beyond simple pipe bombs - with explosive material packed into a piece of tubing and detonated with match heads.
"I think maybe using the bullets maybe shows lack of knowledge, but there is a level of sophistication to everything else we saw in the apartment. Ninety-five percent of the stuff you see is really juvenile and experimental: PVC piping, match head, gun powder," the source said. "But this showed a level of sophistication."
Holmes had been a Ph.D. candidate in neuroscience at University of Colorado-Anshutz Medical Campus.
Rendering the apartment safe was a challenge to seasoned experts, who gained a close look at the devices before defusing them by peering into the apartment from a cherry picker.
After studying the devices, bomb disposal experts used a remote-controlled robot that deployed a 'water shot' that neutralized the control box in the kitchen. They then disposed of the explosives.
They were packed in sand and taken by dump truck to a site east of Denver, where they will be destroyed, the source said.
(Editing by Tim Gaynor and Stacey Joyce)