AURORA, Colo. (AP) — A gunman in a gas mask barged into a crowded Denver-area theater during a midnight premiere of the Batman movie on Friday, hurled a gas canister and then opened fire, killing 12 people and injuring at least 50 others in one of the deadliest mass shootings in recent U.S. history.

When the gas began to spread, some moviegoers thought it was a stunt that was part of the “The Dark Knight Rises,” one of the most highly anticipated films of the summer. Then they saw a silhouette of a person in the smoke near the screen, first pointing a gun at the crowd and shooting.

“There were bullet (casings) just falling on my head. They were burning my forehead,” Jennifer Seeger said, adding that the gunman, dressed like a SWAT team member, fired steadily except when he stopped to reload.