Updated at 6:15 p.m. ET: A law enforcement official said that authorities were facing a challenge in seeking to disarm what appears to be sophisticated explosive booby traps in the apartment of a suspected mass shooter in suburban Denver, NBC News' Pete Williams reported Friday afternoon.
Buildings around the four-story Aurora, Colo., apartment building where James Eagan Holmes lived were evacuated Friday after he said he had explosives in his apartment, police said. Holmes is suspected of opening fire at a midnight premiere of "The Dark Knight Rises," police said. The shooting left 12 dead and 59 others injured.
FBI agents and police used a hook-and-ladder fire truck to reach Holmes' one-bedroom apartment on the third floor, said Oates. By hoisting a camera at the end of a 12-foot pole through a window, officers were able to get a view inside.
Those familiar with what's inside said it's a jumble of apparent trip wires, bottles of liquid and containers of ammunition, fireworks and powders.
"As a layman, it's not something I've ever seen before," said Aurora Police Chief Dan Oates, who added that police were expected to remain on the scene "for hours or days."
There's no way to be certain that the booby traps were genuine, but law enforcers were operating on the assumption that they were, in part because of recent unspecified purchases made by Holmes, NBC News' Williams reported.
The use of trip wires and bottles of liquids suggested a setup that would cause mixing of chemicals that spontaneously ignite, said Carl Knowlen, senior researcher in the Department of Aeronautics and Astronautics at the University of Washington.
The agents might include nitric acid and sulphuric acid, which are readily available in chemical supply stores, he said.
"When mixed with many common substances (these chemicals) spontaneously ignite on contact," he said. "That would be an excellent incendiary source to light off propellants," which could include gun powder or ammunition.
"He had an organic chemistry background and all of these combinations would be familiar to him," said Knowlen. "He may also have known how to formulate it from the diluted stuff you would get at a hardware store."
Law enforcers were moving cautiously for safety reasons and in the effort to preserve as much evidence as possible — things like computers, notebooks and papers that could shed light on Holmes motive and planning.
Authorities still hadn't entered the apartment Friday evening.
"We’re trying to determine how to disarm the flammable or explosive materials in there," FBI Agent James F. Yacone said earlier Friday. "The pictures are pretty disturbing as far as how sophisticated it is. This could be a very long wait."
Yacone said that more than 100 FBI agents were involved in the investigation, as well as personnel from the Bureau of Alcohol, Tobacco, Firearms and Explosives and the Joint Terrorism Task Force, which combines the resources of federal, state and local agencies.
"At this point, we do not see a nexus to terrorism," Yacone said.
Holmes, 24, was arrested behind the Aurora theater. Police said he had two handguns, a shotgun and an assault rifle, at least three of which they believe were used in the attack.
Oates said that Holmes had made a statement to officers about explosives in his apartment. Oates said Holmes also claimed to have explosives in his car, which was parked at the theater, but that proved to be false.
Police evacuated five buildings around Holmes building, starting at about 6 a.m. MT, reported NBC News contributor Bill Briggs, who was on the scene.
Darnell Woods was returning from his overnight shift at a local Home Depot at 6 a.m. and had been in his third-floor apartment across the street from Holmes' building for just a few minutes when he was ordered outside by police.
"They said that we had to get out because they didn't know if his building was going to explode," said Woods, who was sitting on a curb in the hot morning sun, a half block south of Holmes' building on Paris Street. He said he had been perched on that spot since for three and a half hours. He was sweating and wondering when he could return to his apartment.
Holmes had lived in the Aurora apartment building since about May 2011, the Denver Post reported, citing records.
Holmes apartment had always been quiet, according to other tenants in the apartment who spoke to KUSA reporter Jeremy Jojola, so they found it strange when, between midnight and 1 a.m. MT on Friday, there was loud techno music blasting from the apartment.
He was a graduate student in the neuroscience program at the University of Colorado Medical School, a university spokesman told NBC News. He was in the process of withdrawing from school, the university confirmed.
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