The police chief in Aurora, Dan Oates, said in a press conference Saturday that James Holmes' apartment had clearly been rigged ahead of the attack.

"Make no mistake: this apartment was designed … to kill whoever entered it," Oates said. "Who was most likely to enter that location after he planned and executed this horrific crime? It was going to be a police officer."

Also on hand for the press conference was FBI Special Agent James Yacone, whose agency was involved in detonating the bombs. He said a robot was used to enter the apartment and deactivate an explosive device that would have been triggered by a trip wire at the front door.

Other explosive devices and accelerants were also found. A few hours after the initial defusing operation on the apartment began, the Aurora Police Department posted a message to Twitter saying "all hazards have been removed" from the suspect's apartment.

The FBI is continuing to remove evidence from the scene.

Victims' names released

Meanwhile, more details of the attack are emerging, with indications that it had been planned for several months ahead of time. Holmes reportedly ordered several thousand rounds of ammunition legally and had them delivered in multiple shipments.

"He had a high volume of deliveries to both his [school] and home address. We think this explains how he got his hands on the magazines and the ammunition," Oates said, adding there was "evidence of some calculation and deliberation."

Authorities have said Holmes is being held in solitary confinement, a normal procedure in some cases that is designed to protect a suspect from other inmates.

"We typically do this in high-profile cases," Arapahoe County Sheriff Grayson Robinson told Reuters. "It has nothing to do with any specific threat."

The 12 people killed in Friday's shooting were named on Saturday. Among the dead was a six-year-old girl, a teenager, and two US military personnel.

Holmes is scheduled to appear in the Arapahoe County Court on Monday.

mz/jm (Reuters, AP, AFP, dpa)