The number of casualties makes the incident the largest mass shooting in U.S. history.
The suspected gunman was identified as 24-year-old James Holmes, a native of San Diego. Investigators were confident he acted alone and were not looking for any other suspects. There was no immediate word of any motive.
Mourners gathered to remember the victims of the Aurora, Colo., theater shooting at an informal community vigil Friday night.
"When things happen, you realize your humanity a little bit more, and you want to just be with other peole and see what other people are going through," said Stephanie Swihart, who was one of the many people to attend the memorial.
The theater where the shooting took place was the backdrop for the gathering. An official memorial was slated for Sunday.
Holmes is a PhD student who recently withdrew from his neuroscience studies at the University of Colorado. He grew up in San Diego and attended high school there before moving to the Inland Empire, where he graduated from UC Riverside in spring 2010 with a degree in neuroscience. Riverside officials said he had no history of arrest while he lived in the city from 2006 to 2010.
The shooting began around 12:30 a.m. MT Friday at the Century 16 Movie Theaters at the Aurora Town Center, during a midnight showing of "The Dark Knight Rises." It was initially reported that 14 people were killed, but Aurora police revised that figure following further investigation. There were 70 people shot - 10 people were declared dead at the scene, two died at a local hospital and 58 people were injured.
Emergency room doctors at an area hospital confirmed that a 4-month-old was among the victims treated and released. Most of the victims were injured by gunfire but a "handful" during the ensuing chaos, Aurora Police Chief Dan Oates said during a news conference Friday night. One person was hit in an adjacent theater. Thirty people remained hospitalized, 11 of them critical, Oates said.
Authorities had removed all the bodies from the theater by around 5 p.m. MT. Oates said he hoped soon to get a "confirmed list of the 10 deceased and we will begin the agonizing process of meeting with those families and confirming what has happened to their loved ones."
According to ABC News, Holmes bought a ticket to the movie and went into the theater as part of the crowd. After the movie started, he left through an emergency exit and propped open the door. That's when he geared up and re-entered the theater, tossed the gas canister and began shooting.
Holmes was dressed all in black and was wearing a ballistic helmet, a gas mask, ballistic gloves, a bullet-resistant tactical vest and leggings, and throat and groin protection. A witness told ABC News that it all happened during a shooting scene in the movie, leading moviegoers to believe it was some sort of stunt for the film.
"It took me a second to realize what was actually going on," said moviegoer Donovan Tate. "And as people were running away, I hit the ground so I wouldn't be hit."
"I see a guy next to me, a gentleman sitting right next to me getting shot, and then that's when I realized that this is not part of the movie, there's a gunman and he's shooting everyone," said witness Chris Ramos.
Holmes then slowly made his way up and down the theater aisles, shooting at random people - only stopping to reload.
"He ended up shooting people behind me and the bullet casings were just on my forehead, they were burning, I just smelled gunshots," witness Jennifer Seeger told "Good Morning America."
"All I could think was if I stand up he's going to shoot because that's what he was doing, and I was just trying to think how I was going to get my kids out of there," Patricia Legarreta said through tears.
Holmes was apprehended within minutes of the shooting at his white Hyundai parked behind the theater. He did not resist arrest.
He was carrying three weapons, including a .223 caliber Smith & Wesson assault rifle equipped with a drum magazine, which can hold upwards of 100 rounds, a Remington 12 gauge shot gun, and a .40 Glock handgun. A fourth handgun was found in the vehicle.
Holmes had purchased the four guns at local shops and more than 6,000 rounds of ammunition on the Internet in the past 60 days, Oates said at a news conference. All the weapons and ammunition were purchased legally.
Holmes was scheduled to make his first court appearance in Arapahoe County on Monday morning. Charges have not yet been determined, according to the district attorney's office.
According to police sources, Holmes told arresting officers that he was "The Joker." He also spoke of possible explosives in his home. Investigators rushed to the apartment complex, which was quickly evacuated, as well as four other surrounding buildings. Police say the apartment was booby-trapped and loaded with incendiaries and small improvised explosive devices. The ATF has not yet decided how to proceed without setting off explosions.
"The pictures we have from inside the apartment are pretty disturbing considering how elaborate the apartment is booby trapped," police said outside of the apartment complex today. The "flammable and explosive" materials could have blown up Holmes' apartment building and the ones near it, police said.
The apartment complex is home exclusively to University of Colorado Medical Center students, patients, and staff members, residents told ABC News.
The U.S. Department of Defense said three members of the U.S. Armed Forces were wounded in the shooting and one is unaccounted for. One Navy sailor was injured by shrapnel, treated and released. Another sailor who was at the theater early Friday morning cannot be located. The sailors are part of a Navy Cyber Command unit at nearby Buckley Air Force base. Two Air Force airmen were also wounded.
The third installment of the Batman trilogy opened to packed auditoriums around the country at midnight showings and features a villain named Bane who wears a bullet-resistant vest and gas mask. Trailers for the movie show explosions at public events including a football game. Though many moviegoers dressed in costume to attend the opening night screening, police have made no statements about any connection between the gunman's motives and the movie.
The Paris premiere of the movie has been canceled following news of the shooting, and director Christopher Nolan and cast members Christian Bale, Anne Hathaway and Morgan Freeman have also canceled their press interviews.
President Barack Obama addressed the tragedy in remarks in Ft. Myers, Fla. Mr. Obama canceled his Friday campaign event in light of the Colorado shooting and returned to Washington to be briefed.
The president released a statement saying he is "shocked and saddened" by the deadly shooting and urged the nation to "come together as one American family." He said he and first lady Michelle Obama were shocked by the "horrific and tragic" shooting and that his administration will do everything to support the people of Aurora, Colo.
The FBI said there is no indication that the shooting has any connection to terrorism.
A San Diego woman identifying herself as Holmes' mother spoke briefly with ABC News. She had not been contacted by authorities, but when she first heard the news, she immediately expressed concern that her son may have been involved.
"You have the right person," she said, speaking on gut instinct. "I need to call the police. I need to fly out to Colorado."
A neighbor who attended high school with Holmes described him as very smart but didn't really stand out otherwise. Holmes' father Robert was seen leaving his home in the Rancho Penasquitos neighborhood in San Diego with bags packed. Reporters caught up with him at the airport, but he did not have any comment about the incident.
Holmes' family members issued a statement Friday saying their "hearts go out to those who were involved in this tragedy and to the families and friends of those involved" and that they are cooperating with authorities in San Diego and Aurora.
Aurora is located about 10 miles from downtown Denver.
ABC News and the Associated Press contributed to this report.