AURORA, Colo. — Authorities on Saturday 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 Sgt. Cassidee 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 U.S. 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 grimly went door to door late Friday with a list of victims killed in the worst mass shooting in the U.S. in recent years, notifying families who had held out hope that their loved ones had been spared.

The victims included 23-year-old Micayla Medek, said Anita Busch, the cousin of Medek’s father.

“I hope this evil act, that this evil man doesn’t shake people’s faith in God,” she said.

Aurora Police Chief Dan Oates said Holmes used a military-style semi-automatic rifle, a shotgun and a pistol to open fire on the unsuspecting theater-goers. He had bought the weapons at local gun stores within the last two months. He also recently purchased 6,000 rounds of ammunition over the Internet, the chief said.