Aurora shooting suspect planned attack with 'calculation', police say Police detonate explosives found in James Holmes's appartment. Details emerging about the Colorado massacre suspect suggest a budding scientist, brimming with potential, who pursued a graduate programme even as he assembled weaponry he is alleged to have used in a deadly midnight rampage inside an Aurora cinema. James Holmes planned the attack with "calculation and deliberation," police said on Saturday, receiving deliveries by mail that authorities believe armed him and were used to rig his apartment with dozens of bombs. Meanwhile, a federal law enforcement official provided an updated account about the gunfire inside the cinema, saying that a semi-automatic assault rifle used by the shooter jammed during the attack, forcing him to switch to another weapon. The official, who spoke on condition of anonymity in order to discuss the investigation, said the jammed weapon had a high-capacity ammunition magazine. Police have said that a 100-round drum magazine was recovered at the scene and that such a weapon would be able to fire 50 to 60 rounds a minute. In Aurora, investigators spent hours on Saturday removing explosive materials from inside Holmes's suburban Denver apartment a day after police said he opened fire and set off gas canisters in a cinema minutes into a premiere of the Batman film The Dark Knight Rises. The attack left 12 people dead and 58 injured. Holmes's apartment was rigged with jars of liquids, explosives and chemicals that were booby-trapped to kill "whoever entered it," the Aurora police chief, Dan Oates, said. Holmes received several mail deliveries over four months to his home and school and bought 6,000 rounds of ammunition on the internet, Oates said. "He had a high volume of deliveries," Oates said. "We think this explains how he got his hands on the magazine, ammunition," he said, saying this might also be how Holmes got the explosives that were rigged in his apartment. "What we're seeing here is evidence of some calculation and deliberation," Oates added. During the attack early on Friday, Holmes used a military-style semi-automatic rifle, a shotgun and a pistol that he had bought at local gun stores within the past two months, Oates said. Inside the apartment, FBI special agent James Yacone said bomb technicians neutralised what he called a "hypergolic mixture" and an improvised explosive device containing an unknown substance. There also were multiple containers of accelerants. "It was an extremely dangerous environment," Yacone said at a news conference, noting that anyone who walked in would have sustained "significant injuries" or been killed. By late Saturday afternoon, all hazards had been removed from Holmes's apartment and residents in surrounding buildings were allowed to return home, police said. The exception was Holmes's apartment building, where authorities were still collecting evidence. Inside the apartment, authorities covered the windows with black plastic to prevent onlookers from seeing in. Before they did, a man in a Bureau of Alcohol, Tobacco, Firearms and Explosives T-shirt could be seen measuring a poster on a closet that advertised a DVD called Soldiers of Misfortune. The poster showed several figures in various positions playing paintball, some wearing masks. About 8pm on Saturday (3am, Sunday BST), police left the apartment building carrying a laptop computer and a hard drive. Holmes had recently withdrawn from a competitive graduate programme in neuroscience at the University of Colorado Denver, where he was one of six students at the school to get National Institutes of Health grant money. He recently took an intense three-part, oral exam that marks the end of the first year of the four-year programme there, but university officials would not say if he passed, citing privacy concerns. The university said Holmes gave no reason for his withdrawal, a decision he made in June. "The focus of the programme is on training outstanding neuroscientists and academicians who will make significant contributions to neurobiology," the university said. The doctoral programme usually took five to seven years to complete, it said. In a résumé posted on Monster.com, Holmes listed himself as an "aspiring scientist" and said he was looking for a job as a laboratory technician. The résumé, first obtained in Holmes's home state of California by the Press-Enterprise newspaper in Riverside, paints a picture of a brilliant young man brimming with potential: he worked as a summer intern at the Salk Institute for Biological Studies in La Jolla, California in 2006 and mapped the neurons of Zebra finches and studied the flight muscles of hummingbirds while an undergraduate at the University of California, Riverside. He also worked as a cabin counsellor to underprivileged children at a summer camp in Los Angeles in 2008. In a statement, Camp Max Straus confirmed Holmes had worked there for eight weeks. The camp provided no other detail about Holmes but said such counsellors were generally responsible for the care and guidance of roughly 10 children. Neighbours and former classmates in California said although Holmes was very intelligent, he was a loner who said little and was easily forgotten - until this week. Mary Muscari, a criminology professor at Regis University in Denver who studies mass killings, said she was not surprised Holmes was studying neuroscience and mental disorders. "It could be he was interested in that because he knows there's something different in him," she said. Holmes was in solitary confinement for his protection at a county detention facility in the Denver area, held without bond on suspicion of multiple counts of first-degree murder. He was set for an initial hearing on Monday and had been assigned a public defender. Among the deceased victims was a six-year-old girl, and a man who died on his 27th birthday and a day before his wedding anniversary. Families grieved and waited at hospitals, which reported at least seven people still in critical condition on Saturday and others with injuries that were likely to be permanent. Veronica Moser-Sullivan, six, had gone to the movies with her mother, who was drifting in and out of consciousness in a hospital intensive care unit, bullets lodged in her throat and a gunshot wound to her abdomen. "Nobody can tell her about it," Annie Dalton said of her niece, Ashley Moser. She is in critical condition, but all she's asking about is her daughter. Veronica had just started swimming lessons on Tuesday, Dalton said. She was excited about life, as she should be. She's a six-year-old girl," her great aunt said. Alex Sullivan had planned a weekend of fun, celebrating his 27th birthday with friends at the special midnight showing of The Dark Knight Rises and planning his first wedding anniversary on Sunday. "He was a very, very good young man," said Sullivan's uncle Joe Loewenguth. Matt McQuinn, also 27, was killed after diving in front of his girlfriend and her older brother to shield them from the gunfire, said his family's attorney, Rob Scott of Dayton, Ohio. President Barack Obama, who called in his weekly radio address for prayer and reflection on the rampage, was scheduled to travel to Colorado on Sunday to visit the families of victims.