AURORA, Colo. – The shooting suspect who went on a deadly rampage inside a Colorado theater planned the attack with "calculation and deliberation," police said Saturday, receiving deliveries for months which authorities believe armed him for battle and were used to rig his apartment with dozens of bombs.

Authorities on Saturday removed dangerous explosive materials from inside James Holmes' suburban Denver apartment a day after police said he opened fire and set off gas canisters in a suburban theater minutes into the premiere of the Batman film "The Dark Knight Rises." The attack left 12 people dead and 58 injured.

His apartment was rigged with jars of liquids, explosives and chemicals that were booby trapped to kill "whoever entered it," Aurora Police Chief Dan Oates said, noting it would have likely been one of his officers.