Bomb experts disarmed a tripwire and detonated a homemade explosive device Saturday at the home of the man accused of the mass shooting in the U.S. state of Colorado.
Police say the wiring and the incendiary device were "set up to kill" the first person who entered the suspect's apartment. Authorities say experts were proceeding cautiously at midday because the apartment contains other suspicious devices that also may need to be detonated.
Twelve moviegoers were killed and dozens wounded early Friday as volleys of gunfire ripped through a crowded movie theater in Aurora, a city near Colorado's capital, Denver.
Police identify the gunman as James Holmes, 24, student who officials say was preparing to leave a graduate studies program.
Holmes was arrested just outside the theater right after the bloodbath. Police said he had with him a rifle, a shotgun and two handguns, a gas mask and a bulletproof vest.
Officers then surrounded the young man's apartment building about six kilometers from the crime scene, and evacuated all residents.
Investigators said the attacker's motivations remained unclear 36 hours after the movie theater slaughter.
President Barack Obama and one of the top Republican figures in Congress, House Speaker John Boehner, were among leading figures around the nation who have mourned the victims and offered condolences to their families Saturday.
Some information for this report was provided by AP and Reuters.