Onlookers gather outside the Century Aurora 16 theater.
Cell phone video taken by someone at the theater showed scores of people screaming and fleeing the building. Some, like this man, had blood on their clothes.
Police Chief Dan Oates said there was no evidence of a second gunman, and FBI spokesman Jason Pack said it did not appear the incident was related to terrorism.
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- Official: "Imagine that fireball"
- The setup resembled those used in Iraq and Afghanistan, the official says
- Fifteen people remain hospitalized, five in critical condition
- Holmes will be formally charged on July 30
Aurora, Colorado (CNN) -- The suspect in last week's deadly shooting rampage at a crowded Colorado movie theater boobytrapped his apartment with more than 30 homemade grenades and 10 gallons of gasoline, a law enforcement official who viewed video from inside the apartment told CNN Monday night.
The sophisticated set up at the Aurora home of James E. Holmes was meant to harm, or possibly kill, anyone who entered -- and tested the skills of bomb squad members charged with clearing it.
"Imagine that fireball ... you would have an explosion that would knock down the wall of (nearby) apartments," the official said. "That flame would have consumed the entire third floor (of the apartment complex)."
"By the time a fire truck would have arrived, they would have arrived to a building that would have been completely consumed in flames."
The grenades were wired to a control box in the kitchen, which bomb technicians disabled with the help of a remote-controlled robot that squirted water on it.
"It looked like spaghetti," according to the official, who said it resembled setups that are used in Iraq and Afghanistan, but rarely in the United States.
The control box has been sent to Quantico, Virginia, for forensic analysis at the FBI laboratory, the official said.
Over the weekend, Aurora Police Chief Daniel Oates told reporters there was "evidence of, I think, some calculation and deliberation" in the Friday attack at the Century Aurora 16 multiplex.
Holmes received deliveries over the past four months at his home and work addresses, which begins to explain how he may have obtained some of the materials used in the attack and those found at his apartment, Oates said.
The University of Colorado School of Medicine, where Holmes enrolled as a doctoral candidate in its neuroscience program but later withdrew, was investigating whether he received any of the alleged shipments while working as a research assistant at the Anschutz Medical Campus.
Authorities have been tight-lipped about a possible motive in the case, though police spokesman Frank Fania told CNN that Holmes has been uncooperative with investigators and requested an attorney.
The movie multiplex, where the shootings occurred during a midnight screening of the new Batman move "The Dark Knight Returns," will remain shuttered at least until Wednesday to give police time to complete their investigation and allow the suspect's defense team access Tuesday.
Aurora, meanwhile, is bracing for another emotional week as families begin making funeral arrangements. It was not immediately known when the coroner would release the bodies.
On Monday, Holmes made his first court appearance.
Looking dazed at times, Holmes -- who after the attack identified himself to police as "The Joker" -- wore a maroon jumpsuit over a white T-shirt and gave little indication that he was paying attention to the courtroom procedure that ensured he will continue to be held without bond.
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Booking photograph of James Eagan Holmes, accused of killing 12 in Aurora, Colorado Theater Shooting.
He was then led from the courtroom and back to the Arapahoe County Jail, where he is being held in isolation. Formal charges are expected to be filed July 30.
"The charges on which the court found cause included first-degree murder," Arapahoe County District Attorney Carol Chambers told reporters outside the courthouse. She said prosecutors have a lot of work to do.
"I would say there's no such thing as a slam-dunk case," she said. "We're still looking at the enormous amount of evidence."
Deciding whether to pursue the death penalty is a long process that involves input from victims and their relatives, she said.
A capital case would require a finding of either extreme indifference or deliberation, she said.
Holmes is being held in connection with the shootings that killed 12 people and left 58 others wounded. As of late Monday, at least 15 people remained hospitalized -- five in critical condition -- in four area hospitals.
Four of those killed were active members of the the U.S. military. The Department of Defense is flying flags at half-staff in their honor.
"These acts of heroism and sacrifice are the essence of what military service is about -- putting your life on the line to defend those who are part of the American family," Secretary of Defense Leon Panetta said in a statement Monday.
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Meanwhile, Lisa Damiani, an attorney representing the Holmes family but not the suspect, said his family members were keeping their location secret. "I don't think they would like the media to know where they are," she said, adding that she feared for their safety.
"They're doing as well as they can, under the circumstances," Damiani told reporters at her office in San Diego, California, where the family lives. "I think everyone can imagine how they're feeling -- anyone who's ever been a parent."
She added, "The family has elected not to discuss James or their relationship with James at this time."
The family issued a statement Friday saying, "Our hearts go out to those who were involved in this tragedy and to the families and friends of those involved." It added, "We are still trying to process this information."
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This story was written by CNN's Ed Payne in Atlanta, with reporting from Poppy Harlow in Aurora. CNN's Josh Levs, Tom Watkins, Dana Ford, Joe Sutton, Ed Lavandera, Nick Valencia, Kathleen Johnston, Drew Griffin, Don Lemon and Susan Candiotti contributed to this report.
