AURORA, Colo. - Whoever set up the explosive booby traps in James Holmes' third-storey apartment was hoping to kill a cop, according to Aurora's police chief.

"Make no mistake, OK? This apartment was designed ... to kill whoever entered it, and who was most likely to enter that location after he planned and executed this horrific crime? It was going to be a police officer," said a candid Police Chief Dan Oates Saturday afternoon.

"If you think we're angry, we sure as hell are angry about what has happened to our city, what has happened to these wonderful people who live here and also what he threatened to do to one of our police officers."

Holmes, who was arrested early Friday morning, is the lone suspect in the midnight movie massacre that has left 12 dead and 58 others wounded, though he has not been convicted of any crime.

Early reports indicate he told police after his arrest that his apartment was booby-trapped, and local and federal bomb experts have been slowly working their way into the 800-square-foot tenement that they say is packed with trip wires and explosives.

Saturday afternoon, bomb experts successfully deactivated a trip wire linked to a fire bomb just inside Holmes's door. Reports indicate there are other triggering devices - wires and fuses - inside the apartment, as well dozens of incendiary and explosive devices.

FBI agent Jim Yacone described the explosive set-up as "certainly sophisticated."

"The threat has not been completely eliminated. It has been significantly reduced," Yacone said.

But as Oates lashed out at Holmes's alleged plot to kill a cop, Aurora's fire chief Mike Garcia reminded residents that the Denver-area streets are safe and they shouldn't be afraid.

"I just don't want this shameless and senseless act of one man to make this difficult for families to move on" with their lives, he said. "What makes Aurora an all-American city is how we handle these crises and these challenges. Go out and see a movie. Go out into your city. Don't be afraid."

There are four other cinemas in Aurora showing the new Batman movie, and Oates has said there will be a police presence at those cinemas "in an abundance of caution."

Police are also hoping to finish their investigation at the Century 16 cinema and turn it over to the owners Wednesday, meaning it could reopen then.

The mall to which the Century 16 theatre is attached attached to the theatre where the shooting took place was open on Saturday.