AURORA, Colorado (AP) — Authorities began the intricate process of disarming booby traps in the apartment of the suspect behind the Colorado movie theater rampage, hoping to find clues inside to the motive for the shootings without causing an explosion that could destroy key evidence.

Scores of law enforcement officials, including bomb squad technicians and dozens of federal agents, removed one trip wire and one explosive device inside James Holmes' apartment Saturday, and "other devices" are in there, Aurora police Sergeant Cassidee Carlson said.

"We have been successful in defeating the first threat," Carlson said. The traps were meant to kill the first people entering the apartment, she said.

Holmes, 24, was arrested early Friday outside the suburban Denver theater with high-powered weapons and ammunition and charged with the rampage that killed 12 and injured 58 during the midnight showing of the new Batman movie, "The Dark Knight Rises."

Makeshift memorials sprang up for the victims, including a US navy sailor, an aspiring sportscaster and a man celebrating his 27th birthday. In his Saturday radio address, President Barack Obama urged Americans to pray "for the victims of this terrible tragedy, for the people knew them and loved them, for those who are still struggling to recover."

Seven of the wounded remained in critical condition on Saturday, some with injuries that could be permanent, a trauma surgeon said.

Police have been unable to enter Holmes' apartment after learning it had been booby-trapped with trip wires and possible explosives, and evacuated several buildings around it.

Experts entered the apartment and began to disarm the trip wires one by one to render them harmless, hoping not to detonate anything that could eliminate evidence against the suspect or information about a motive.

"We don't want to lose evidential value," Carlson said.

About 30 ammunition shells and up to 30 other devices in the apartment also need to be disarmed, she said.

"A controlled detonation or another triggering mechanism" might be required, she said.

Police grimly went door to door late Friday with a list of victims killed in the worst mass shooting in the US in recent years, notifying families who had held out hope that their loved ones had been spared.