"The shooting happened during a battle scene on screen so it took some time to realize that is wasn't part of the special effects," one witness said to the Scripps' station in Denver, Colo.
Aurora police said 12 people died and at least 38 people were injured. Those numbers have been reduced since the initial reports of 14 deaths and about 50 injuries.
According to a mortician called out to the scene, a person went into the movie theater, set off a smoke grenade and started firing.
That witness say the gunman walked toward the front of the theater and fired into the back of the theater.
"Everybody thought it was fireworks," said Chris Jones, one of the people in theater nine where the shooting happened.
Jones said he didn't see the gunman, he only saw a spark in the corner of the theater.
"The lights never came on," Jones said. "When the shooting cleared, we just ran. When we got outside, it was chaos."
Jones said he thought it was someone playing around. After he realized it wasn't stopping and people were screaming, he got on the ground.
Jones said he heard 20 to 30 rounds in a minute or two.
Officials say the bullets went through the wall of theater nine, where the shooting occurred, and into the neighboring theater. One witness named Laurie said she was in the theater next door, when the shooting started.
"There was a shooting scene in the movie, at the same time, there was a gun shot, a real one," Laurie said.
Laurie said when her friend turned towards her, part of a bullet had hit her friend in the mouth.
Laurie and she and her friend ran out the exit doors and saw people running and screaming. She said her friend is OK.