'Dark Knight Rises' Shooting: Interior of James Holmes' Apartment Revealed

James Holmes

"It was absolutely chilling," "Dateline's" Chris Hansen says of all the explosives, which "could have taken the building down."

Dateline's Chris Hansen got a peek inside James Holmes' apartment on Sunday, and what he saw was "absolutely chilling."

On Friday, the 24-year-old allegedly opened fire at the Century 16 movie theater in Aurora, killing at least 12 people ranging in age from 6 to 51 and injuring some 58 others during a midnight screening of The Dark Knight Rises.

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Hansen was allowed to watch a law enforcement videotape that has not been released for broadcast and shared what he saw with viewers of the NBC News program.

"In the middle of his living room are dozens of black softball-shaped firework shells that he bought filled with explosive powder," he said. "They are all over the place. In the middle there are two jars full of liquid wires, as I said, all over the place there was a black box with a red blinking light. A mechanical camera then pans over on top of a glass table -- you see this water cooler jug half full of bullets. Then you pan down, then you see this black box with another red blinking light."

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"The camera goes over, there are two chairs, one has a jar apparently with fluid. The other has another black box and then there are green soda pop bottles filled with fluid all the way around."

Hansen added that he saw the trip wire, made of fishing line, that was across the front door. It was about 2 or 3 feet off the ground and rigged to explode as soon as someone opened the door, he said.

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"It could have taken the building down," Hansen said. "It was very sophisticated and very powerful."

Holmes is set for an initial hearing at 9:30 a.m. Monday at the Arapahoe County Courts.