AURORA, Colo. - 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.

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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.