Officers were finally able to enter the third-floor apartment today with the assistance of federal explosives experts, the Denver Post reported.
They had to disarm one device and destroy another in a controlled explosion.
The apartment contained dozens of home-made booby-traps constructed from liquid explosives, chemical, powders and bullets, according to the Washington Post.
Whoever planted them apparently wanted to "kill and maim any first responders or anyone that came in there," a law enforcement official told the paper.
Police were able to photograph the inside of the apartment yesterday using a camera attached to a pole and inserted through a window.
Aurora Police Chief Dan Oates told reporters that he had never seen anything like it, according to CBS News.
Holmes, 24, was taken into custody in a parking lot behind the movie theater where he allegedly shot 70 people, at least 12 of them fatally, early Friday morning.
He warned police that his apartment contained explosives, but since then is said to have stopped cooperating with authorities. He also reportedly calls himself "the Joker."
Former classmates and neighbors told NBC News they remembered Holmes as a quiet, intelligent and unassuming person.
Police have refused to comment on any possible motive. They say that, in the past 60 days, Holmes had purchased four guns and more than 6,000 rounds of ammunition, Reuters reported.
Holmes is due to appear in court on Monday morning.