The attack on Batman fans took place just a few miles from the scene of one of America's most notorious shooting sprees.
In 1999, teenagers Eric Harris and Dylan Klebold shot themselves after killing 12 students and a teacher at Columbine High School, in Littleton, another suburb of Denver about 25 miles from the Century 16 cinema in Aurora where the latest massacre happened.
Heavily armed, Harris and Klebold roamed the school firing indiscriminately. The Columbine shootings left America in shock and led to demands for tighter gun controls.
But those demands have always been fiercely resisted by America's powerful gun lobby, which sees the bearing of arms as a constitutional right.
Critics say President Barack Obama has failed to fulfil his promises to improve weapons safety.
But his rival in the next race for the White House, Republican Mitt Romney, has courted the gun lobby, headlining the annual convention of the powerful National Rifle Association in April even as controversy raged over the shooting in Florida of unarmed black teenager 17-year-old Trayvon Martin.
Politics aside, shooting sprees are a fact of life in the US. Just three days ago, 17 people were hurt - two critically - after a gunman fired into a crowded bar in Tuscaloosa, Alabama, before shooting at people as they ran out.
In May, a gunman killed five people in a shooting spree before turning the gun on himself in Seattle.
A month earlier, expelled Korean adult student One L Goh shot dead seven people at Oikos University in California after being teased over his poor English skills.
That so-called campus massacre brought back memories of the worst attack of its kind in American history, the 2007 Virginia Tech shooting spree when gunman Seung-Hui Cho killed 32 people and wounded 25 others before committing suicide.