The horror happened at a midnight showing of the new Batman movie, starring Christian Bale, near Denver, Colorado on Friday (20Jul12).
A masked man wearing body armour and wielding a rifle and two handguns entered the cinema in the town of Aurora via an emergency exit and threw tear gas or smoke bombs before opening fire.
Officials confirmed 14 people have died and up to 50 others, including four children, have been taken to hospital. One of the dead is said to be a six-year-old child.
Witnesses reported some of the injured were in an adjacent cinema and were hit by bullets which penetrated a dividing wall, and several people were injured when they tried to protect a child the gunman had turned his sights on.
A suspect in his early 20s has been taken into custody and cops launched a search for explosives in a nearby car park.
Video footage taken by a stunned cinemagoer moments after the horror shows dazed patrons fleeing the building, some of them spattered with blood.