Updated Saturday, 4:05 p.m. PST
Just before 12:30 a.m. MT, alleged shooter James Holmes bought a ticket to the late-night screening of "The Dark Night Rises" and entered the Century Aurora 16 theater in a mall in the Denver suburb of Aurora, Colorado, the AP reported.
He went into the theater and propped open a back exit door. When he returned to the theater he was dressed in all black combat gear and wore a gas mask.
As moviegoers in Theater 9 settled into their seats, Holmes, 24, allegedly threw two explosive canisters containing an irritant gas before opening fire, shooting "many, many rounds," police said.
"We have no capability right now of calculating that number," Police Chief Dan Oates said at a press conference Friday, fielding a question about the exact number of shots Holmes allegedly fired.
Moviegoers dropped to the ground as bullets flew through the air striking victims. Some rounds penetrated the walls of the theater, striking at least one person in the adjacent screening room, Oates said.
By 12:39 a.m., police received multiple 911 calls about the shooting.
Police arrived at the theater complex at 14300 E. Alameda Ave. within minutes of the calls, Oates said, with 150 to 200 officers eventually on the scene.
Ten people died in the theater. Two more died after being transported to area hospitals. Fifty-eight were wounded.
It is unclear when the gunman stopped firing and returned to his car.
K9 teams surrounded the mall and a team of officers located a white Hyundai coupe outside the theater, where Holmes was waiting with a small cache of weapons and a gas mask.
Two federal authorities confirmed to ABC News said Holmes claimed to be "The Joker" and dyed his hair to match Batman's arch nemesis from "The Dark Knight," the penultimate installment in the trilogy. "The Dark Knight Rises" is the final installment.
He did not put up a fight as police arrested him and confiscated a Remington 12-gauge shotgun, an AR-15 assault rifle and two .40-caliber pistols.
Holmes left one of the pistols in the car during the shooting, Oates said.
Police and rescue workers rushed to evacuate the wounded.
At about 9:45 a.m. MT, President Barack Obama spoke from Ft. Myers, Fla., where he was scheduled to make a campaign stop. He offered his condolences and reflecting on his personal feelings as he talked about savoring his daughters' embraces tonight.
Republican presidential front runner Mitt Romney also issued a similar statement at a press conference and called the shooting an "unspeakable tragedy.
Both candidates agreed to suspend campaigning and yank ads from the airwaves in Colorado, vowing to keep their mudslinging away from the grief-stricken state.
At the same time, police began surrounding Holmes' apartment building (pictured left) on nearby Paris Street, a few blocks away from the scene of the carnage.
Police said Holmes admitted the apartment was booby trapped and SWAT teams and bomb squads were proceeding with extreme caution.
By about 11:45 a.m., Gov. John W. Hickenlooper, the former mayor of Denver, called the shooting an "act of depravity" at a press conference with Aurora Mayor Steve Hogan and Oates, who gave an update about the situation.
Oates provided details on the suspect's background. Holmes grew up in San Diego and graduated from the University of California, Riverside with a degree in neuroscience. He was going to graduate school at the University of Colorado pursuing a PhD in neuroscience but was in the process of withdrawing from school.
Meanwhile, Arlene Holmes, a San Diego woman who identified herself as the alleged gunman's mother, told ABC News that her son was likely the culprit and that "You have the right person."
The family soon after issued a statement saying their hearts went out to victims.
The alleged shooter's father, Robert Holmes, arrived at Denver International Airport from San Diego at about 2:15 p.m., TMZ reported. The first off the plane, he was escorted by police to a black SUV on the tarmac.
At 4:15 p.m., after hours of processing the crime scene, the Denver Post reported that authorities had begun removing the 10 bodies of victims who died in the theater.
After clearing the area, authorities began breaking into the suspect's apartment about 4:45 p.m. as techno music blared from the windows. The unit was so extensively booby-trapped that authorities could not safely defuse the devices, police told Reuters. They planned to use a robot to set off the explosives.
Holding back tears as he recalled his officers' efforts to save the wounded, Oates held another press conference at 7 p.m., saying authorities were working with grieving families to identify victims. He said a prayer vigil would be held later Friday night.
He said the police usually provide security at the theater on weekends.
"This was a Thursday night," he said. "But we were there in 90 seconds."
As bomb experts surveyed the scene inside the apartment Friday evening, they found a web of booby traps so elaborate they delayed entering until morning.
Police and authorities entered the apartment early Saturday morning with a robot and disabled a tripwire stretched across the front door of the 800-square-foot dwelling. Next, they defused the trigger on a volatile mixture of chemicals that, if triggered, would have exploded in a blast or ignited.
Oates said the bomb team will soon enter the apartment to neutralize any remaining traps and collect evidence, which will be processed at the high-level security Marine Corps base at Quantico.
After encountering the deadly devices in Holmes' apartment, blocks away from the theater, Oates was visibly angered at a 2 p.m. press conference Saturday afternoon.
"If you think we're angry," he said, "we sure as Hell are angry."
He was joined by FBI special agent James Yacone, who said that he and has team have encountered many improvised explosives but "rarely anything this complex."
By late Saturday afternoon, federal and local bomb experts were planning to move into the apartment, confident that all major theats had been neutralized, police said.
Police also said the Arapahoe County coroner's office released the names and ages of all 12 victims who died.
The youngest identified victim was a six-year-old girl.
Her name was Veronica Moser and she was shot alongside her mother, Ashley, 25. The little girl died at the scene, and her mother, who is slipping in and out of consciousness at a nearby hospital, does not yet know her daughter died.