A heavily armed gunman tossed tear gas into an Aurora, Colo. move theater, then sprayed the audience with gunfire during an early morning screening of the new Batman movie, authorities said. Twelve people died and 50 were wounded.

One of the wounded victims 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. The suspect was not immediately identified, though Fania said he was believed to be in his early 20s.

“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.

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 issued a statement saying 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,” it 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.

Witnesses told KUSA that the gunman kicked in an emergency exit door and threw a smoke bomb into the darkened theater before opening fire. A federal law enforcement official told CNN the smoke bomb described by witnesses was tear gas.

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

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

“We just heard a pop, pop, pop, pop,” said Quentin Caldwell, who was attending the Batman showing in an adjacent theater.

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.”

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, the federal law enforcement official told CNN.

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. They also are conducting emergency traces on the weapons used to see how they were obtained, he said.

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 Lanigan.

Several people remained in critical condition at area hospitals, however.

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 of them in critical condition, five in fair, said Shelly Davis, house supervisor.

Swedish Health Center spokeswoman Nicole Williams said her hospital was treating three people, two of them in critical 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.

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 wounding 23 others before killing themselves.

Warner Bros. issued a statement Friday morning following the mass shooting at a Colorado movie theater during a showing of “The Dark Knight Rises,” saying, the company “is deeply saddened to learn about this shocking incident. We extend our sincere sympathies to the families and loved ones of the victims at this tragic time.”