Aurora, Colorado movie theater shooting timeline

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AURORA, Colo.-- Police in Aurora, Colorado said 24-year-old James Holmes opened fire during the premiere of the new Batman movie just after midnight on Friday, July 20.

In all, 12 people were killed and at least 58 others hurt – many with critical injuries. Holmes was arrested near his car outside the theater, but the challenge for police came in rendering his booby trapped apartment safe for investigators and the neighborhood where he lived.

Inside, police found explosives and unknown chemicals, which were later detonated.

The police chief in Aurora said investigators are building a case to show that the suspect in the Colorado theater shooting is a very intelligent person who methodically plotted the attack.

Chief Dan Oates told CBS' "Face the Nation" on Sunday police will be going over items taken from his apartment over the next couple of days.

Oates said he had never seen a booby trap as elaborate as what was found in Holmes' apartment, noting that a second triggering mechanism was found.

Oates said the setup speaks volumes about Holmes' intelligence, deliberation and cold-bloodedness.

He said an FBI behaviorist is helping in the investigation.

The University of Colorado says it's investigating whether the suspect used his position as a graduate student to order materials in the potentially deadly booby traps that police say they found in his apartment.

Police say Holmes received deliveries over four months to his home and school. They haven't identified the contents.

University spokeswoman Jacque Montgomery says Sunday the school is looking into those packages received at the school.

Montgomery says Holmes had withdrawn from the university's Ph.D. neuroscience program without giving a reason.

A U.S. Navy veteran who served three tours of duty in the Middle East. A 6-year-old girl excited about her swimming classes. A Target employee who shielded his girlfriend and her brother with his own body. They and nine others were killed in the shooting rampage during a midnight showing of "The Dark Knight Rises" in a Denver suburb.

Below is a timeline showing the events associated with the developments in this case.