Authorities say he booby-trapped his apartment with explosives, then traveled to the movie theater armed with four weapons, tear gas and body armor planning to kill audience members during a screening of "Batman: The Dark Knight Rises."
Witnesses who have spoken to CNN about the shooting have said the gunman roamed the theater, shooting randomly as people tried to scramble away or cowered between seats.
Among the 41 calls to 911, one stands out. In the 27-second call, at least 30 shots can be heard amid the chaos.
At his preliminary hearing in January, police who responded described hellish scenes inside the theater and described finding Holmes, dressed in body armor, standing outside, seeming "detached from it all," according to Officer Jason Oviatt.
At the conclusion of the brief hearing, the father of one of the victim's shouted out, "Rot in hell, Holmes."
Holmes' trial date has been set for August 5.