AURORA, Colo. -- A neuroscience graduate student in a gas mask barged into a crowded Denver-area theater during a midnight showing of the Batman movie on Friday, hurled a gas canister and then opened fire, killing 12 people and injuring 58 others in one of the deadliest mass shootings in recent U.S. history.

The suspect, 24-year-old James Holmes was soon arrested. Investigators later learned his apartment four miles away from the theater was booby trapped.

When the smoke began to spread inside the theater, 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. They saw a silhouette of a person in the haze 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.

Every few seconds it was just: Boom, boom, boom, she said. He would reload and shoot and anyone who would try to leave would just get killed.

Authorities did not release a motive in the shooting. The FBI said there was no indication it is tied to any terrorist groups.

Holmes had an assault rifle, a shotgun and two pistols, and wore body armor a federal law enforcement official said, speaking on the condition of anonymity to discuss the ongoing investigation.

FBI agents and police used a hook and ladder fire truck to reach Holmes' apartment in suburban Denver, Aurora police Chief Dan Oates said. They put a camera at the end of 12-foot pole inside the apartment, and discovered that the unit was booby trapped. Authorities evacuated five buildings as they determine how to disarm flammable and explosive material.

Victims were being treated for chemical exposure apparently related to canisters thrown by the gunman. Some of those injured are children, including a 4-month-old baby who was released from the hospital.

Aurora Police Chief Dan Coates says the last of the 10 deceased victims from the midnight showing of a Batman movie was removed from the theater Friday afternoon.

Coates says officers expect to get a confirmed list of the deceased and meet with their families Friday night.

In addition to the 10 people who died at the theater, two others later died from their injuries.

The movie opened across the world Friday, with midnight showings in the U.S. The shooting prompted officials to cancel the Paris premiere, with workers pulling down the red carpet display at a theater on the famed Champs-Elysees Avenue. Guards were at a screening at a movie theater in New York's Times Square.

Friday's attack began shortly after midnight at the multiplex theater at a mall in Aurora, the state's third-largest city. Witnesses who fled the theater described it as not the safest in Aurora to Denver's KUSA.

The film has several scenes of public mayhem -- a hallmark of superhero movies. In one scene, the main villain Bane leads an attack on the stock exchange and, in another, leads a shooting and bombing rampage on a packed football stadium.

It was the final installment of the Dark Knight trilogy directed by Christopher Nolan, starring Christian Bale as Batman. The series has a darker tone than previous Batman incarnations. It is the follow-up to The Dark Knight, which won Heath Ledger a posthumous Oscar for his searing portrayal of The Joker.

The gunman released a gas that smelled like pepper spray from a green canister with a tag on it, Seeger said.

I thought it was showmanship. I didn't think it was real, she said.

Seeger said she was in the second row, about four feet from the gunman, when he pointed a gun at her face. At first, I was just a deer in headlights. I didn't know what to do, she said. Then she ducked to the ground as the gunman shot people seated behind her.

She said she began crawling toward an exit when she saw a girl about 14 years old lying lifeless on the stairs. She saw a man with a bullet wound in his back and tried to check his pulse, but I had to go. I was going to get shot.

Witness Shayla Roeder said she saw a young teenage girl on the ground bleeding outside the theater. She just had this horrible look in her eyes .... We made eye contact and I could tell she was not all right, Roeder said.

Police, ambulances and emergency crews swarmed on the scene after frantic calls started flooding the 911 switchboard, officials said. Officers came running in and telling people to leave the theater, Salina Jordan told the Denver Post. She said some police were carrying and dragging bodies.

Hayden Miller told KUSA-TV that he heard several shots. Like little explosions going on and shortly after that we heard people screaming, he told the station. Hayden said at first he thought it was part of a louder movie next door. But then he saw people hunched over leaving theater.

Officers later found the gunman near a car behind the theater.

Holmes enrolled last year in a neuroscience Ph.D. program at the University of Colorado-Denver but was in the process of withdrawing, according to school officials, who didn't provide a reason.

Police released a written statement from Holmes' family: Our hearts go out to those who were involved in this tragedy and to the families and friends of those involved.

Police found a gas mask, rifle, handgun and at least one additional weapon inside the car, Oates said, adding that there was no evidence of any other attackers.

A law enforcement official briefed on the investigation told The Associated Press that 24-year-old James Holmes has asked for a lawyer.

The official spoke on condition of anonymity to discuss the ongoing case.

A large truck lettered bomb squad arrived near an Aurora apartment complex where the suspect is believed to have lived, about four miles from the theater. Dozens of police squad cars, vans and other vehicles were already at the scene, along with black-clad officers carrying automatic weapons.

Police evacuated residents of the building. The official who spoke on the condition of anonymity also says police found jars of chemicals in Holmes' booby trapped Aurora apartment with wires nearby. Oates said police also checked for explosives in the parking lot and at the Century 16 theater and secured those areas.

Coates says there are 70 victims but not all were shot. Eleven are in critical condition.

President Barack Obama said he was saddened by the horrific and tragic shooting, pledging that his administration was committed to bringing whoever was responsible to justice, ensuring the safety of our people, and caring for those who have been wounded.

It was the worst mass shooting in the U.S. since the Nov. 5, 2009 attack at Fort Hood, Texas, when an Army psychiatrist killed 13 soldiers and civilians and more than two dozen others wounded.

In Colorado, it was the deadliest since the Columbine High School massacre on April 20, 1999, when two students opened fire at the school in the Denver suburb of Littleton, killing 12 classmates and a teacher and wounding 26 others before killing themselves.

Warner Bros. and the filmmakers are 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, the studio said.

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