ABC

This morning on "This Week," Pierre Thomas, senior justice correspondent for ABC News, told me that, according to sources, a Batman poster and a computer were found in the apartment of Aurora mass shooting suspect James Holmes.

"I was struck by one source today who said that this 'was really like a mad scientist, really like a villain in a movie,'" Thomas said. "We are being told by sources that they have found the computer, and also a poster of Batman."

ABC News previously reported that Holmes told authorities after the shooting that he "was The Joker." The Joker, played by the late Heath Ledger, was the villain in the second film of Chris Nolan's Batman trilogy.

On Friday, 24-year-old James Holmes allegedly entered a movie theater in Aurora, Colo. during a midnight showing of "The Dark Knight Rises" and opened fire, killing 12 people and injuring dozens more. The incident is the largest mass shooting in American history.

Thomas described Holmes' planning as "cold-blooded, meticulous," with him taking months to amass his arsenal.

"He developed an execution plan that he put in place that worked to perfection, according to my sources," Thomas said. "Also, the time and effort in terms of putting together that booby-trapped apartment shows the intensity and focus."

Officials have said that Holmes' intelligence is "what made him so dangerous."

"One cop I talked to yesterday said, look, most criminals are stupid. This guy was thoughtful, brilliant," Thomas said.

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