US President Obama has paid tribute to the victims of the Aurora shooting spree and said the federal government would do "everything necessary to bring whoever is responsible for this heinous crime to justice."
Twelve people were killed and 58 more wounded in a shooting rampage at a screening of the new Batman film, the Dark Knight Rises at a cinema in Aurora.
Residents of Aurora staged a vigil last night as the community begins to absorb the shock of the tragedy.
Armed with an assault rifle, a shotgun and a pistol, Aurora police chief Dan Oates said the suspect fired "at a rapid pace" in the cinema and "purchased 6,000 rounds of ammunition" on the internet "legally" before the attack.
Officers said they arrived at the scene within 90 seconds after receiving the first emergency calls.
The police quickly took 24-year-old suspect James Eagan Holmes into custody in a parking facility behind the cinema, where he surrendered without a fight.
Holmes, a graduate student who authorities said had his hair dyed red and called himself "the Joker" in a reference to Batman's comic-book nemesis, is due to make his first court appearance on Monday at 09:30 local time (15:30 GMT).
Police said Holmes had also booby-trapped his Aurora apartment with what appeared to be sophisticated explosives, creating a potential hazard for law enforcement and bomb squad officers who swarmed to the scene.
Authorities also evacuated five nearby buildings and created a perimeter of several blocks as they planned to detonate the suspected explosives with a robot, Oates said.
I am proud of the men and women of your police and fire department.
Colorado Governor John Hickenlooper also praised the efforts of the Denver community following the gunman's rampage in the city.
The 60-year-old said the response of the federal government had been "unbelievable" and everybody is trying to move forward. He went on to challenge the community to "rise back and lift ourselves above this".