"I don't know how else to explain it. It's horrific," said Tracy Lauzon, director of EMS and trauma services at Aurora Medical Center.
Oates said the man was wearing a ballistic helmet and protective gear for his legs, throat and groin, black gloves and a gas mask.
Jennifer Seeger, who survived the attack, said she had seen the man and thought his get-up was part of the entertainment for the film's debut.
She said the man first shot toward the ceiling, then began shooting at people. He reloaded during his attack, she said.
"He was just literally just massacring anybody that got up that was trying to run away," Seeger said.
As of Friday afternoon, 30 people remained hospitalized, 11 of them in critical condition, according to Colorado Gov. John Hickenlooper.
Holmes is scheduled to appear in an Arapahoe County, Colorado, courtroom Monday morning, Rob McCallum, spokesman for the Colorado Judicial Department, said Friday. The court file was sealed, according to a court order. He is being held in the Arapahoe County jail, Oates said.
A statement from Holmes' family in San Diego asked for "privacy during this difficult time."
"Our hearts go out to those who were involved in this tragedy and to the families and friends of those involved," the statement said, adding, "We are still trying to process this information."
The FBI is assisting in the investigation, officials said, though it did not appear that the incident was related to terrorism.
Prior to Friday's shooting, Holmes' criminal record in Aurora consisted only of a traffic summons.
President Barack Obama canceled campaign events Friday, telling supporters at what had been scheduled as a rally in Fort Myers, Florida, that "there will be other days for politics."
"This will be a day for prayer and reflection," he said, calling for the country to unite as one and support the victims.
Flags at the White House were lowered to half-staff Friday afternoon in honor of the victims.
A law enforcement source said two of the guns used in the attack were purchased at a Bass Pro Shop in Denver, while the two others were bought at separate Gander Mountain Guns outlets in the area. Investigators also found a drum magazine, capable of carrying 100 rounds of ammunition, which was attached to the AR-15 rifle, two law enforcement officials said.
A statement from Bass Pro Shops said its Denver store followed appropriate protocol on the sale of the two weapons.
Authorities also searched the suspect's car in the parking lot of the movie theater and found more magazines and ammunition, a federal law enforcement official said.
"It was everywhere," the official said.
Christopher Nolan, director of "The Dark Knight Rises," condemned the shooting as "savage" and "appalling."
"The movie theatre is my home, and the idea that someone would violate that innocent and hopeful place in such an unbearably savage way is devastating to me," Nolan said in a statement on behalf of the cast and crew of the film. "Nothing any of us can say could ever adequately express our feelings for the innocent victims of this appalling crime, but our thoughts are with them and their families."
Four Aurora theaters showing "The Dark Knight Rises" will have extra security for the foreseeable future "out of an abundance of caution," Oates said.
Warner Bros., the studio behind the film, canceled the movie's Paris premiere, while New York police Commissioner Raymond Kelly said his officers would watch over screenings of "The Dark Knight" in the city to prevent copycat shootings. AMC Theatres, meanwhile, said it would not permit guests in costumes that make others uncomfortable, nor will it allow face-covering masks or fake weapons.
Aurora, a Denver suburb, is about 13 miles from Littleton, Colorado -- site of the April 1999 Columbine High School massacre.
In that incident, two teenage students, Dylan Klebold and Eric Harris, armed themselves with guns and bombs and shot people inside the high school. They killed 13 and wounded 23 before killing themselves.
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