Bomb experts disarmed a tripwire and set off a controlled explosion in the booby-trapped apartment of mass shooting suspect James Holmes Saturday, slowly working their way into the home of the failed neuroscience student being held in custody after Friday's theater massacre.

Detectives had been unable to investigate Holmes' 800-square-foot third-floor apartment because of the elaborate web of incendiary and chemical devices, numbering about 60 in all.

The effort to defuse and disarm the explosives was made all the more delicate by the need to preserve any criminal evidence.

In a hallway just inside the front door, a filament trip wire was strung at waist height, according to a law enforcement source. The trip wire was connected to two containers of chemicals that, when mixed, could create an explosion.

The bomb squad disarmed the setup by sending in a robot that slipped beneath the trip wire and removed one of the bottles of liquid.

Then came 30 spherical canisters in the living room. These resembled fireworks shells packed with gunpowder -- "improvised grenades," the official called them. Wires ran from these devices to a "control box" in the apartment kitchen. It was not clear, the official said, how they were supposed to be detonated.

Authorities used a "bottle shot" -- a small explosive charge that sends out a wave of water at high speed -- to destroy the control box.

Finally, the official said, there were about three jugs in the living room filled with what appeared to be a combination of liquid and gunpowder. "Improvised napalm," the official called it. These were not rigged to blow up, but probably would have been set off in a "sympathetic detonation" if the other explosives had been tripped. That would have given the blast extra heat and destructive power.

Officials said the bomb squad had largely succeeded in disarming the explosives. The next step is to let residents return to four adjacent buildings; some neighbors have been staying in emergency shelters and others with friends and relatives during the bomb squad efforts.

"It went very, very well. The threat has not been completely eliminated. It has been significantly reduced," FBI Special Agent James Yacone said Saturday afternoon.

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