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WARNING: GRAPHIC CONTENT

Witnesses to the horrific massacre at a midnight showing of “Batman: The Dark Knight Rises” in Colorado described a chaotic and terrifying scene as movie patrons fled for their lives when a gunman opened fire, killing at least 12 people.

The gunman, identified by federal law enforcement officials as James Holmes 24, was masked and wore black clothes when he set off some sort of explosive and then opened fire in one of five theaters in the complex that was hosting a midnight showing of the movie, witnesses told reporters.

James Wilburn was sitting in the second row of theater 9 after midnight when an emergency door opened and a man entered, the Denver Post reports.

"He was dressed in black," Wilburn told the newspaper. "Wearing a flack jacket and a gas mask."

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Holmes was carrying a shotgun and had a rifle strapped to his back, Wilburn said. The gunman then dropped a canister, causing a noxious gas to spew out. He raised the shotgun and repeatedly fired toward the back of the theater.

Wilburn and three friends dove to the floor, hiding behind seats in front of them. The gunman was only five or six feet away, he said.

Once the shotgun was empty, the gunman calmly dropped it to the floor, took the rifle and went on firing. Wilburn heard roughly 30 shots, the Denver Post reports.

Meanwhile, 21-year-old Naya Thompson and her 22-year-old boyfriend Derrick Poage were running for their lives. Thompson said the gas spread and the gunman may have dropped two canisters.

"It was like a tear gas," Thompson told the newspaper. "I was coughing and choking and I couldn't breathe."

Benjamin Fernandez, 30, told the Denver Post he was watching the movie when he heard several explosions. He said that people ran from the theater and there were gunshots as police shouted 'get down!"

The theater was packed, and there were many children in attendance, according to witnesses. Abenezer Mergia, 18, told Fox News Channel most viewers were between ages 15 and 25, and that the shooting

“It was probably from 15 to 25, that was the majority.

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"They were just expecting everybody to get to their car and just get out. Everybody that was hurt – there was blood everywhere. It was crazy.”

Jaime Marshall told Fox News Channel she was in an adjacent theater when explosions rang out during a shooting scene in the blockbuster film.

“We thought someone was just pranking us in the movie,” she said. Then, a man ran in and told people to get out, she said. “He said, ‘Don’t walk through the lobby, someone’s shooting.’”

She said when the lights came on, she saw bullet holes that had come through from the adjacent theater where the shooting took place. “We saw a girl who had been shot in the leg, and people covered with blood,” she said.

Police told reporters the gunman had two guns and set off an explosion before firing on people at random in theater 9.

"Witnesses tell us he released some sort of canister," Aurora Police Chief Dan Oates. "They heard a hissing sound and some gas emerged and the gunman opened fire."

Salina Jordan, 19, told the paper she was in Theater 8 and saw people hit in her theater. She said one girl was struck in cheek, others in stomach including a girl who looked to be around 9 years old.

Jordan said it sounded like firecrackers until someone ran into Theater 8 yelling "they're shooting out here!"

A witness who was in the same adjacent theater told WDVR-31 bullets penetrated the wall between the two rooms

“They said bullets were flying through the wall,” the witness said. Then, gesturing to her friend, she said, “the girl that was sitting next to her got hit in the jaw.”

Darrell Wilmoth, a former military man who was in Theater 9, told Fox News Channel, the theaters were packed with young people.

"The sad part is the majority of the theater was kids. It was just, crazy," he said. "My concern was just, getting those kids that were injured up to the ambulances. And praying. That's what I'm doing now, praying for those kids that were injured."

Tammi Stevens told the Denver Post her son, 18-year-old Jacob Stevens, was inside Theater 9 when the shooting started. He survived and later told her he saw a man clad in body armor walk into the theater and throw some sort of canister that then emitted some sort of gas.

"You let your kids go to a late night movie ... you never think something like this would happen," Stevens said.