The gunman reportedly never said a word while shooting 71 people, killing 12, in a soldout show for "The Dark Knight Rises."
A graduate student's attack in a sold-out theater near Denver showing the new Batman movie, in which 12 people were killed early Friday, was the culmination of two months of meticulous planning that included a potentially deadly booby trap left in the suspect's home for investigators, authorities said.
Fifty-eight other people were injured, many of them seriously, in the shootings shortly after midnight at the Century 16 Movie Theaters complex in Aurora, Colo. Earlier reports had said 59 people were injured, but police revised that number at a news conference Friday night. All but a small handful of the injured had been shot, Police Chief Dan Oates said.
Thirty people remained in area hospitals Friday night, 11 of them in critical condition, after a carefully orchestrated attack in which the suspect, identified as James Eagan Holmes, 24, bought all of his weapons and ammunition legally beginning in May.
Late Friday, the family of Alex Sullivan, 27, said in a statement that he was among the dead, the Denver Post and The Associated Press reported. Heart-wrenching photographs taken earlier Friday showed Sullivan's father, Tom, grieving and pleading for information about his son.
Federal and local enforcement officials said Holmes was sheathed in a helmet, a gas mask, a tactical bulletproof vest, throat and groin protectors and tactical gloves. All of the gear was black.
Holmes was armed with two .40-caliber Glock handguns, a Remington 870 single-barrel pump shotgun, a Smith & Wesson AR-15 assault-style rifle and as many as 6,000 rounds of ammunition, Oates said.
The scene also appeared to have been specially targeted for maximum carnage — the local premiere of one of the most eagerly awaited movies of the year, "The Dark Knight Rises," the third in the series of director Christopher Nolan's Batman films.
In a statement, Nolan expressed "profound sorrow at the senseless tragedy that has befallen the entire Aurora community."
After he was arrested outside the theater, Holmes told police that he was the Joker, a reference to one of the most prominent villains in the Batman canon, a law enforcement official told NBC News on condition of anonymity. (The official said the suspect had dyed his hair red or orange, which isn't typically associated with the green-haired Joker character, who doesn't appear in "The Dark Knight Rises.")
Aurora police said Holmes also booby-trapped his apartment with an elaborate network of wire-connected bottles containing an unknown liquid, presumably intended to go off when authorities arrived to canvass his home.
Holmes told police about the trap before they arrived, however, and investigators hadn't entered the apartment Friday night. They were analyzing gases and examining photographs of the scene to figure out how to deal with the materials and had decided to defer any action until Saturday at the earliest, Oates said.
"It's not something I've ever seen before," said Oates, who said that the area was evacuated and that police were expected to remain on the scene "for hours or days."
Holmes, a graduate student from San Diego who was in the process of withdrawing from the neuroscience program at the University of Colorado-Denver medical school, put up no resistance when he was arrested in a parking lot at the theater, police said. He retained legal counsel and wasn't answering investigators' questions, they said.
"We are confident he acted alone," Oates said of Holmes, who was scheduled to appear in Arapahoe County District Court on Monday morning to face unspecified charges. Authorities refused to speculate on his possible motive.
One of those killed was Jessica Ghawi, a sportswriter whosurvived a June 2 mass shooting at a mall in Toronto in which two people were killed and seven others were injured. Ghawi blogged under the name Jessica Redfield.
Defense officials told NBC News that a sailor at Buckley Air Force Base in Aurora was missing and presumed to have been killed. A second sailor and two airmen from Buckley were also shot. Their identities and conditions weren't available.
Authorities said the gunman appeared at the front of the theater at 12:39 a.m. (2:39 a.m. ET), about 20 minutes into the film, and released two canisters of gas. Witnesses told reporters that the gunfire erupted during a shootout scene. Authorities responded within a minute and a half, Oates said.
"It was mass chaos," witness Jennifer Seeger told TODAY. The gunman shot the ceiling and then "he threw in the gas can, and then I knew it was real."
Witnesses said the gunman entered the theater at Aurora Town Center through an emergency exit door. But a federal law enforcement official told The Associated Press that the suspect bought a ticket and went in as part of the crowd. He is believed to have propped open an exit door as the movie was playing, the official said.
Aurora is a suburb less than 10 miles east of downtown Denver and just 15 miles northeast of Littleton, near the scene of what had been the worst mass shooting in Colorado: the Columbine High School massacre on April 20, 1999, when two gunmen killed 12 fellow students and a teacher and wounded 26 other people before killing themselves.
Three of the suspect's four weapons were found in his white Hyundai parked at the back entrance to the theater; one of the handguns was found in the theater.
Law enforcement officials told NBC News that the weapons were legally bought from local stores of two national chains — Gander Mountain Guns and Bass Pro Shop — beginning in May.
Oates didn't say what kind of magazines were used, but he said "many, many rounds were fired." Some rounds penetrated an adjoining theater and injured at least one person, he said.