Colorado Movie Shooting: 'What a Miracle It Wasn't Worse'

VIDEO: David Muir has complete coverage of the tragic shooting.
WATCH Aurora, Colorado Shooting: The Next Day

Colorado officials are crediting the first responders of Aurora for the only thing that might be called a "silver lining" in the horrific shooting at a movie theater that left 12 dead and 58 injured.

"What a miracle it wasn't worse," Colorado Gov. John Hickenlooper said today.

Ambulances arrived at the scene in two and a half minutes, and got injured victims to hospitals "incredibly rapidly," the governor said.

"If there's a silver lining, it's that we didn't lose more lives, and it's because our responders not only did their job, they went above and beyond," said Aurora mayor Steve Hogan.

Former doctoral student, James Holmes, 24, is suspected of open firing in a packed midnight screening of the latest Batman movie. According to police sources, Holmes told the officers arresting him that he was "The Joker," referring to the villain in the second installment of the Batman movie trilogy, "The Dark Knight."

Holmes also warned police that he had booby-trapped his apartment, leading officers to evacuate the Aurora apartment building. Police said the apartment was "set up to kill."

Bomb technicians used a robot to secure a safe entry into the apartment Saturday morning, removing a trip wire and one explosive device. A bomb squad then spent most of the rest of the day disarming the 30 various devices inside the apartment and an additional 30 aerial shells.

"It was an extremely dangerous environment. If a neighbor or unassuming pedestrian would have walked in that door or God forbid a first responder they would have sustained significant injuries and/or a loss of their life," FBI Agent Jim Yacone said.

Did Holmes Try to Lure Neighbors Into His Apartment?

Authorities believe that Holmes tried to lure his neighbors into his apartment during the shooting Friday morning.

Kaitlyn Fonzi, who lives directly below Holmes's apartment, told ABC News that around midnight, she heard very loud music coming from the apartment above her.

The "same techno song that sounded like it included gunshots was playing in a loop for a long time," she said.

Fonzi knocked on the door and when no one responded, she put her hand on the door knob, and then decided not to open it.

Fonzi said the music abruptly stopped at about 1 a.m.

Another neighbor, Chris Rodriguez, told ABC News affiliate KMGH-TV in Denver that he and his girlfriend also heard loud techno music coming from above them at midnight.

"Usually the complex is very quiet, nobody has parties, so that was the first time we actually had a party or a lot of noise at the complex," Rodriguez said.

After about 15 minutes, Rodriguez's girlfriend went upstairs and knocked on the door.

"She went upstairs to the apartment, and she knocked on the door pretty hard, she knocked two or three times and yelled into the door, 'Hey, can you turn that music down, we are trying to sleep,'" said Rodriguez.

Rodriguez said no one answered and his girlfriend didn't hear any footsteps, but she noticed that the door moved.

"The door moved a little bit, and the handle jiggled a little, and she was contemplating going into the apartment, but something told her don't do it," Rodriguez said.

"My theory is that what he did is he started the music up around midnight so somebody would go up to the apartment and open that door around 12:15," Rodriquez said.

ABC News affiliate KMGH-TV contributed to this report.