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.
An online seller of tactical police gear confirmed it sold more the $300 worth of equipment to Holmes on July 2. The equipment from TacticalGear.com included an assault vest, magazine pouches and a knife.
The company issued the following statement in regards to the purchase:
"Everyone at TacticalGear.com is shocked and appalled that the alleged shooter purchased tactical gear from us for use in this horrific attack. We process thousands of orders a day which include this type of equipment. We primarily serve members of the armed services and law enforcement professionals. Our thoughts and prayers are with the victims and their families."
View the receipt here
Police say 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Montgomery says Holmes had withdrawn from the university's Ph.D. neuroscience program without giving a reason.
(KUSA-TV © 2012 Multimedia Holdings Corporation with The Associated Press)