Colorado police probing the deadly mass shooting at a movie theater outside Denver say bomb experts have eliminated all major explosives threats at the booby-trapped apartment of the suspect.

Aurora Police Chief Dan Oates spoke Saturday afternoon, after bomb squads disarmed a tripwire and detonated a homemade explosive device at the apartment near Friday's crime scene. Oates told reporters the apartment was rigged to kill whomever first entered it. He said in all likelihood that would have been a police officer.

Twelve moviegoers were killed and dozens wounded early Friday as a gunman sprayed scores of bullets into a crowded theater.

Police identified the suspect as James Holmes, a 24-year-old student whom officials say was preparing to withdraw from a graduate studies program.

The heavily-armed Holmes was arrested just outside the theater right after the bloodbath, in possession of a rifle, a shotgun, 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.

Police said the attacker's motivations remained unclear, nearly two days later.

President Barack Obama and one of the top Republican figures in Congress, House Speaker John Boehner, were among national leaders who have publicly mourned the victims and offered condolences to their families.