(CNN) — A heavily armed gunman attacked an Aurora, Colorado, movie theater early Friday, tossing tear gas before opening fire on the terrified audience and killing 12 and wounding 38, authorities said. The theater was showing the new Batman movie, “The Dark Knight Rises.”

Witness recalls chaos after gunman bursts into theater

One of the injured was just 3 months old, according to hospital workers.

Police arrested a man believed to be the shooter in a rear parking lot of the theater, Frank Fania, a police spokesman, told CNN.

“He did not resist. He did not put up a fight,” Fania said. Police seized a rifle and a handgun from the suspect, and another gun was found in the theater, he said.

Two federal law enforcement sources involved in the investigation identified the suspect as James Holmes, 24, of Aurora, Colorado.

KMGH: Mass shooting inside Aurora movie theater

Aurora Police Chief Dan Oates said there was no evidence of a second gunman, and FBI spokesman Jason Pack said it did not appear the incident was related to terrorism.

President Barack Obama said he and first lady Michelle Obama were “shocked and saddened” by the shooting and pledged the administration’s support for victims of the shooting.

“As we do when confronted by moments of darkness and challenge, we must now come together as one American family,” Obama said.

Chaos broke out during the showing of “The Dark Knight Rises” at the Century Aurora 16 theater when the shooting began, police and witnesses said.

Police said the gunman appeared in the front of the theater and threw a smoke bomb before opening fire. A federal law enforcement official told CNN the smoke bomb described by witnesses was tear gas.

It was unclear how the man got into the theater, but witnesses told CNN affiliate KUSA that he came in through an emergency door.

One movie-goer, who was not identified, told KUSA the gunman was wearing a gas mask.

KUSA: One person in custody

Some people in the audience thought the thick smoke and gunfire was a special effect accompanying the movie, police and witnesses said.

The smoke smelled like a Fourth of July firework, said CNN iReporter Adam Witt. It took a few gunshots before he figured out what was going on.

“There were so many people running,” he said. “I didn’t look back. I just remember getting up from the floor and shouting, ‘We have to run.'”

Witt said he held his wife’s hand as they rushed out of the theater.

“There was a moment where I lost her hand, but I grabbed her shirt,” he said. “We didn’t let go of each other.”

Quentin Caldwell, who was attending a screening in the adjacent theater, said he wasn’t sure at first what was going on, despite hearing a “pop, pop, pop, pop” sound.

“We really didn’t know something was happening until someone came from the left entrance and said we should not go outside because somebody with a gun was out there,” he said.

Armed guards appeared at the theater exit and demanded audience members raise their arms to ensure they were not carrying weapons, then told them to run, Caldwell said.

“Outside was chaos. There was wounded everywhere,” he said.

Cell phone video taken by someone at the theater showed scores of people screaming and fleeing the building. Some had blood on their clothes.

One police officer carried a girl believed to be about 9 with gunshot wounds to her back out of the theater, a witness said. “She wasn’t moving.”

Witness: ‘We have to run’

Officers rushed many of the wounded to hospitals in their patrol cars.

Authorities also have evacuated the suspect’s Aurora apartment building after he made a statement about explosives in his unit, Oates said.

The shooter used at least four guns — an “AK type” rifle, a shotgun and two handguns, a federal law enforcement official told CNN. The source also said the shooter used tear gas.

Bureau of Alcohol, Tobacco and Firearms agents have searched the suspect’s car and went to his home to search for explosives, agency spokesman Tom Mangan said.

Law enforcement officers who searched the suspect’s apartment found “items of interest,” a federal law enforcement source involved in the investigation told HLN. He did not elaborate.

A woman who lives across the street from where the suspect is believed to live said her building was evacuated by police around 4 a.m.

“They told us there was a bomb or bomb material located in the house across the street from us.” Rebecca Bradshaw said.

In addition to looking into the possibility of explosives, ATF agents also are conducting emergency traces on the weapons used to see how they were obtained, Mangan said.

KWGN: Witnesses first thought gunfire was part of movie

Police initially said 14 people had died — 10 in the theater and four at area hospitals, but revised the death toll to 12 later Friday morning, according to Aurora Police Lt. Jad Lanigan.

Several people remained in critical condition at area hospitals.

Of the wounded, at least 20 were being treated at the University of Colorado Hospital, said spokeswoman Jacque Montgomery. All of the wounded suffered from gunshot wounds, which ranged from minor to critical, she said.

“They’re arriving by police, by ambulance. Some are walking in,” she said.

The victims being treated there ranged in age from 3 months to 45, the hospital said.

Denver Health Center had six patients from the shooting, one in critical condition and five in fair condition, said Shelly Davis, house supervisor.

Swedish Health Center spokeswoman Nicole Williams said her hospital was treating three people, two of them in critical condition and one in fair condition. A fourth patient was on the way, she said.

Parker Adventist Hospital was treating two people for minor injuries, according to a spokeswoman.

Hundreds of police officers descended on the theater, and the FBI has joined the investigation.

“We were calling for help from every police and fire agency,” Fania said.

Warner Bros., the studio behind the movie, said the company and filmmakers were “deeply saddened” to learn of the incident. The studio canceled the movie’s Paris premiere, while New York police Commissioner Raymond Kelly said his officers would watch over screenings of “The Dark Knight” to prevent copycat shootings.

Aurora, a Denver suburb, is about 13 miles from Littleton, Colorado — site of the April 1999 Columbine High School massacre.

In that incident, two teenage students, Dylan Klebold and Eric Harris, armed themselves with guns and bombs and opened fire inside the high school. They killed 13 people and wounded 23 others before killing themselves.

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