Q: WHAT HAPPENED?

A: Shortly after midnight Friday, a gunman wearing a gas mask and black SWAT gear set off a gas canister and then opened fire inside a crowded theater in the Denver suburb of Aurora, Colo., killing 12 people and wounding nearly 60 others, authorities said. The suspect was arrested near a car behind the theater and identified as 24-year-old James Holmes. Authorities did not release a motive. The FBI said there was no indication of ties to any terrorist groups.

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Q: WHO IS THE SUSPECT?

A: Holmes was studying neuroscience in a Ph.D. program at the University of Colorado-Denver but was about to drop out. He enrolled in June 2011 but left a year later, though it wasn’t immediately clear why.

He played soccer at Westview High School in the San Diego area and graduated with honors from the University of California, Riverside, in spring 2010 with a bachelor’s degree in neuroscience.

Those who knew Holmes described him as a shy, intelligent man who grew up in San Diego with parents who were active in their well-to-do suburban neighborhood.

Police in San Diego read a statement from family members in which they said their hearts go out to those involved. The family said they’re cooperating with authorities in San Diego and Aurora, and are trying to process everything.

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Q: WHAT IS GOING ON AT HOLMES’ APARTMENT?

A: Police said the third-floor apartment was booby trapped, so they’ve evacuated five surrounding buildings and bomb technicians were determining how to disarm flammable or explosive material.

“It’s a pretty extensive booby trap. We’re not sure what it’s attached to. There are trip wires. There are three containers and we don’t know what it’s inside,” said Chris Henderson, deputy Aurora fire chief.

The apartment is about four miles from the theater.

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Q: ARE MOVIE THEATERS STILL SHOWING THE FILM?

A: Yes, though theaters and police increased security and AMC Theaters, the nation’s second-largest chain, barred customers from wearing masks or costumes. Some fans were nervous about going to see the film, but many were undeterred.

At theaters from New York to Texas, police increased their presence as a response to the shootings. At the Regal Gallery Place multiplex in downtown Washington, theater employees searched patrons’ bags and purses while taking their tickets.

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Q: WHO WAS HURT IN THE THEATER?

A: Many victims treated at hospitals were under 40, including a 4-month-old baby and 6-year-old. The oldest reported patient was 45.

Victims were treated for chemical exposure, apparently related to canisters thrown by the gunman, and gunshot and shrapnel wounds. Eleven remain in critical condition.

The Defense Department said two sailors and an airman were wounded and one sailor was unaccounted for in the shooting.

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Q: WAS THERE ANY LINK BETWEEN THE SHOOTING AND THE MOVIE?

A: It’s unclear. New York City’s police commissioner said he was told the gunman had painted his hair red and called himself the Joker — Batman’s nemesis — but Aurora police would not confirm that.

In “The Dark Knight Rises,” a masked villain leads a murderous crew into a packed football stadium and wages an attack involving guns and explosives. But violent attacks on the public by villains are key components of most superhero movies.

There are general parallels to the shooting, “The Dark Knight” and the comic book character. Bruce Wayne’s drive to become Batman arose from witnessing the deaths of his parents at the hands of small-time criminal who shot and killed them after they had left a movie theater. The Batman video game called “Arkham City” takes place in an abandoned movie theatre.

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Q: HOW MANY GUNS DID THE SUSPECT HAVE?

A: Officers found an AR-15 assault rifle — the civilian form of the M-16 — a Remington 12-gauge shotgun and a .40-caliber Glock handgun in the theater and another identical handgun in the car. The gunman also set off two devices that released a smoke or an irritant, Aurora Police Chief Dan Oates said.

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Q: WHEN WAS THE LAST MASS SHOOTING IN THE U.S.?

A: The massacre in Aurora was one of the deadliest in the U.S., and 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 shooting 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.