The University of Colorado said it's investigating whether shooting suspect James Holmes 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 said 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.

Police sidy Holmes opened fire in a theater during a packed midnight showing of the new Batman movie early Friday, killing 12 and injuring 58. It took hours for bomb experts to dismantle a complicated web of trip wires and explosives inside his apartment.

Montgomery said Holmes had withdrawn from the university's Ph.D. neuroscience program without giving a reason.