AURORA, Colorado // Bomb-squad technicians yesterday removed a trip wire and defused an explosive booby-trap in the apartment of the man accused of killing 12 people in a gun rampage in a cinema.
The trip wire "clearly was intended to kill", said local police sergeant Cassidee Carlson. "This is serious stuff."
James Holmes, 24, has been in custody since he was arrested in the car park of the Aurora cinema outside Denver, Colorado, after the gun attack early on Friday at a packed midnight premiere of the new Batman movie, The Dark Knight Rises.
Twelve people were killed and 58 injured in the attack. Some were hurt in the chaos that ensued as the audience tried to flee the smoke-filled cinema in a panicked dash for the doors. Among the injured, 11 are in a critical condition.
The four weapons recovered after the attack were bought legally by Mr Holmes in the past two months.
"All the weapons that he possessed, he possessed legally," Aurora police chief Dan Oates said. "And all the clips that he possessed, he possessed legally. And all the ammunition that he possessed, he possessed legally."
A spokesman for a Denver gun shop said they had sold a shotgun and a Glock pistol to Mr Holmes. "Background checks, as required by federal law, were properly conducted, and he was approved."
Mr Oates said the gunman used a military-style semi-automatic rifle, a shotgun and a pistol, and had also recently bought 6,000 rounds of ammunition over the internet. Mr Holmes had enrolled last year in a neuroscience doctoral programme at the University of Colorado-Denver, though he left the programme last month for unknown reasons. In academic achievement, "he was at the top of the top", said Timothy P White chancellor at the University of California, Riverside, where Mr Holmes earned his undergraduate degree before attending the Denver school.
Mr Holmes's stellar academic record, shy demeanour and lack of a criminal background made the attack even more difficult to fathom.
Nor is it known why he chose a cinema to stage the assault, or whether he intended some twisted, symbolic link to the film itself.
The new Batman movie, the last in the trilogy starring Christian Bale, opened worldwide on Friday with midnight showings in the US. The plot has the villain Bane facing Bale's Caped Crusader with a nuclear weapon that could destroy all of fictional Gotham.
In reaction to the shooting Hollywood studios aligned in a rare show of solidarity to give their weekend box-office reporting a rest. Sony, Fox, Disney and Universal joined the distributor Warner Bros in withholding their box-office numbers for the weekend. Warner said on Friday it would forgo the usual revenue reports until Monday out of respect for the victims and their families.
Warner Bros also cancelled appearances in Mexico by the cast and filmmakers.
Near the entrance to the cinema car park, a makeshift memorial of 12 candles sat in a row near piles of flowers yesterday.
Tanner Coon, a 17-year-old Aurora resident who was watching the film with two friends, said he first thought the gunshots were firecrackers. When he realised what was happening, he ducked between the seats and waited for the shooter to say what he wanted.
The shooting was the worst in the US since the attack on November 5, 2009, at Fort Hood, Texas. An army psychiatrist was charged with killing 13 soldiers and civilians and wounding more than two dozen others. It was the deadliest in Colorado since the 1999 attack at Columbine High School, where two students killed 12 classmates and a teacher and wounded 26 others before killing themselves.
* With additional reporting by Reuters and Agence France-Presse