It may be that the apartment James Holmes lived in was as frighteningly wired as his brain.
It was certainly intended to be as deadly, police say, as it was rigged up with layers of booby traps that would have greeted anyone who entered with deadly web of trip wires, explosives and jars of fuel.
"Make no mistake … this apartment was designed … to kill whoever entered it," Aurora Police Chief Dan Oates said on the weekend, after Mr. Holmes, 24, was arrested at the end of Friday's mass shooting at the premier of the new Batman movie in Aurora, Colo., a Denver suburb. "And who was most likely to enter that location after he planned and executed this horrific crime? It was going to be a police officer."
Chief Oates, a square-jawed former New York Police Department officer with a law degree and a cool, intense gaze, was clearly upset that a trap had been set for his officers.
"If you think we are angry, we sure as hell are angry," he said.
But Chief Oates and FBI Special Agent James Yacone made it clear that with a slow and methodical approach, the apartment that Mr. Holmes had turned into a spider's nest of traps had been carefully unwound by a team of police officers, FBI bomb experts and fire fighters.
"We've got the bomb guys next to the fire guys. … Before the bomb guy makes a decision he consults the fire guy," said Sergeant Cassidee Carlson of the Aurora police.
Agent Yacone, who has had experience neutralizing an array of expertly rigged explosive devices overseas, said that "rarely anything this complex" had challenged him before.
He said there were "multiple booby traps," starting with a wire strung across the front door and apparently meant to incinerate anyone who entered.
Sgt. Carlson, in a briefing outside the apartment, just before the operation began, said it would unfold in phases.
"The most immediate threat is the trip wire, the booby trap," she said. "[Neutralizing] that may also involve a controlled detonation … once that trip wire is dealt with they'll move on to disposal."
She said experts had identified at least 30 improvised explosive devices that would be gingerly removed by a robot, placed in a large truck filled with sand, and taken to an empty field outside of Denver to be destroyed.
The operation began with bomb experts using a firetruck bucket to reach Mr. Holmes's third floor apartment. They broke the rear windows and then photographed as much as they could of the 800 square foot interior. In addition to the battered couch and bike found in a student's flat, they saw a confusing array of jars and containers thought to contain explosive fuels.
Using a robot, law enforcement officials gently probed the apartment, disarming devices as they were encountered, but also retrieving evidence along the way in case a bomb exploded and destroyed material that might be used in the prosecution of Mr. Holmes.
"This was certainly challenging. . .it went seamlessly," he said.
During the afternoon there was one small, muffled explosion in the apartment. The controlled blast was detonated by bomb experts, but authorities declined to say what they blew up.
Chief Oates said investigators have learned that Mr. Holmes had "a high volume of [package] deliveries to both his work and home address" several weeks before he launched his gun attack.
"We're seeing evidence … of some calculation," he said.
Police have said the suspect stockpiled 6,000 rounds of ammunition, but they would not say if he'd also ordered bomb-making materials through the mail.
Chief Oates declined to discuss what police investigators might have learned from questioning Mr. Holmes, but he made it clear they are trying to figure him out.
"The FBI behavioural analysis unit are very much plugged in … to try and find out wha this motivation was," he said.
That might not be easy, even though Mr. Holmes's father was brought to Denver on the weekend, apparently to help police.
The man accused of perpetrating Colorado's worst mass killing was not well known in Aurora. Even in his own building, where neighbours say he would walk past without acknowledging them.
That's unusual in Denver, a city that prides itself on western hospitality and where complete strangers wish you a good day on the street.
He lived in a three-story, red brick walk up just off busy Peoria Street. It is an older neighbourhood, somewhat run down, but showing signs of renewal as younger people move into the area.
But it has its problems, as a "Gang-Free Zone" sign posted outside a school just a block away suggests.
"You hear shots fired and have no idea what's going on, but we've had few shootings, really, over the years," said Charles Snyder, an engineer who lives not far from Mr. Holmes's apartment building. "It's pretty quiet. I've been here 30 years."
He said the neighbourhood is diverse, with white, black and Hispanic people living as neighbours.
"At first glance people are a little scared of it," said Diane Snow of the neighbourhood.
She owns and rents out a small house just down the street from the bomb-rigged apartment, but lives herself in an upscale part of the city.
"And I'll tell you what: This is a friendlier neighbourhood," she said. "People talk to you.
When the police showed up [to block the street while bomb crews worked on the apartment] the neighbours across the street cooked the police officers food and brought them water."
Ms. Snow, and Sylvia Pagel, a long time resident, said they had never run in to Mr. Holmes, a quiet man who must have tried hard to keep a low profile in such an open community.
Recinos Habrhan, who was forced to evacuate his home while bomb crews worked on the apartment, said he recognized Mr. Holmes when he saw him on newscasts.
"I don't talk to him; only see him sometimes," he said "I can't believe it."
Jackie Mitchell told The Denver Post that he'd had drinks with Mr. Holmes at a local bar,but never saw any signs that he was a troubled individual.
"He just didn't seem the type to go into a movie theatre and shoot it up. He seemed like a real smart dude," he said.
But postings Mr. Holmes apparently made on an adult dating site suggest some thing might have been amiss.
"Will you visit me in jail?" asks an individual who identified himself as ClassicJimbo, a 24-year-old looking for "a fling or casual sex gal."
The site contained a photo of Mr. Holmes, with his hair dyed orange. Police have said he referred to himself as the Joker, when arrested outside the theatre.
Mr. Holmes grew up in San Diego, and went to the University of California Riverside,where he graduated with honours, before enrolling last year at Colorado University, where he was one of only six students to win a National Institute of Health grant to conduct neuroscience research. The program he was in focuses on the physical mechanics of the brain.
A university spokesman said he withdrew last month, and it was not thought he'd had access to campus buildings since then. Just to be sure, however, police used bomb dogs to sweep through the buildings he'd worked in. They found nothing. Apparently everything he'd received in packages at the research lab he had access to was taken home, to his booby-trapped apartment.