U.S. President Barack Obama flew to Colorado for a few hours on Sunday to comfort the families of those who died in Friday's movie-theatre shooting in a Denver suburb, and he also visited a hospital where injured victims are being treated.

He visited with each family of the 12 people killed when a gunman opened fire at the premiere of the new Batman movie, he said, and some of the 58 people who were wounded.

"I come to them not so much as president as I do as a father and as a husband," Obama said afterward. "It was an opportunity for families to describe how wonderful their brother or their son or daughter was, and the lives that they had touched, and the dreams that they held for the future."

The president said he told the families that while the media spotlight is on the perpetrator for now, eventually the shooter's presence in the collective mind will fade, and "what will be remembered are good people who were impacted by this tragedy."

The visit comes as authorities are peeling back the layers in their investigation into the life of the suspect in the shooting rampage, which occurred early Friday morning at a screening of The Dark Knight Rises.

U.S. President Barack Obama speaks Sunday evening alongside Colorado Senator Mark Udall, left, and state Gov. John Hickenlooper at the University of Colorado Hospital in Aurora. He said the country will be thinking about the Aurora massacre victims 'each and every day.' (Saul Loeb/AFP/Getty)

The University of Colorado said Sunday it was examining whether the accused, James Holmes, used his position as a graduate student to order materials in the potentially deadly booby traps that police said they found in his apartment.

Details about Holmes suggested he was a budding scientist who pursued a graduate program, even as he assembled weaponry he would allegedly use in the deadly midnight rampage inside an Aurora movie theatre.

Holmes, 24, got deliveries over four months to his home and school, authorities have said. He bought thousands rounds of ammunition as well and an urban assault vest, two magazine holders and a knife for just over $300 on July 2, from an online supplier of tactical gear for police and military personnel, the company said.

"He had a high volume of deliveries," Aurora Police Chief Dan Oates said. "We think this explains how he got his hands on the magazine, ammunition," he said, as well as the rigged explosives in his apartment."

Candles, flags, and other tributes have been left at the scene of a movie theatre in Aurora, Colo., where a gunman killed at least 12 people Friday in one of the deadliest mass shootings in recent U.S. history. (Alex Brandon/Associated Press)

Holmes was not co-operating with officials as he was being held in solitary confinement at a Denver-area county detention facility, Oates said. "He lawyered up. He's not talking to us," the chief said.

Investigators found a Batman mask inside Holmes's apartment after they finished clearing the home of booby traps and ammunition, a law enforcement official close to the investigation said Sunday on condition of anonymity because he was not authorized to speak to the news media.

It also emerged Sunday that Holmes had applied to become a member at a local gun range, but his strange behaviour caused concern, the facility's owner said.

Glenn Rotkovich said Holmes emailed an application to join the Lead Valley Range in Byers on June 25. Rotkovich followed up by calling Holmes' apartment to invite him to a mandatory orientation the following week. He said the phone message was "bizarre — guttural, freakish at best."

Rotkovich told his staff to watch for Holmes at the July 1 orientation and not to accept him into the club.

'Calculation and deliberation'

Holmes allegedly planned the attack with "calculation and deliberation," police said Saturday, receiving deliveries by mail that authorities believe armed him for battle and were used to rig his apartment with dozens of bombs.

Meanwhile, The Associated Press reported that a federal law enforcement official provided an updated account about the gunfire inside the theatre, saying that a semi-automatic assault rifle used by the shooter jammed during the attack, forcing him to switch to another weapon.

Sports blogger Jessica Ghawi was killed in the mass shooting at a screening of the latest Batman movie in Denver. (Twitter)

The official, who spoke on condition of anonymity to in order to discuss the investigation, told the wire service that 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.

Booby-trapped to kill

His apartment was rigged with jars of liquids, explosives and chemicals that were booby-trapped to kill "whoever entered it," Oates said, noting it would have likely been one of his officers.

Inside the apartment, FBI Special agent James Yacone said bomb technicians neutralized 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 afternoon, all hazards have been removed from the Holmes' apartment and residents in surrounding buildings were allowed to return home, police said.

The exception was Holmes' apartment building, where authorities were still collecting evidence. Inside the apartment, authorities began covering the windows with black plastic to prevent onlookers from seeing in. Before they did, a man in an ATF 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.

Suspect an 'aspiring scientist'

About 8 p.m., police left the apartment building carrying a laptop computer and a hard drive.

Holmes had recently withdrawn from a competitive graduate program 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 program 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.

'He always had a smile, always made you laugh. He had a little bit of comic in him'—Joe Loewenguth, uncle of shooting victim Alex Sullivan

"The focus of the program is on training outstanding neuroscientists and academicians who will make significant contributions to neurobiology," the university said. The doctoral program usually takes five to seven years to complete, it said.

In a resumé posted on Monster.com, Holmes listed himself as an "aspiring scientist" and said he was looking for a job as a laboratory technician.

The resumé, first obtained by The Press-Enterprise 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 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.

Counsellor to underprivileged kids

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 are generally responsible for the care and guidance of roughly 10 children.

Neighbours and former classmates in California said although Holmes was whip-smart, he was a loner who said little and was easily forgotten — until this week.

James Holmes, 24, is the suspect in a shooting attack that killed 12 people in a suburb of Denver. (The University of Colorado/Reuters)

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 Saturday, held without bond on suspicion of multiple counts of first-degree murder. He was set for an initial hearing on Monday and has been appointed 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 still in critical condition Saturday and others with injuries that likely are permanent.

Veronica Moser-Sullivan, 6, 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.

A blogger and aspiring sportscaster who recently wrote of surviving the Eatons Centre shooting in Toronto in early June was also among those killed. The death of Jessica Ghawi, who was also known as Jessica Redfield, was a "complete and utter shock," said her brother, Jordan Ghawi.

Another victim, 27-year-old Matt McQuinn, 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.

Alex Sullivan had planned a weekend of fun, first ringing in his 27th birthday with friends at the special midnight showing of The Dark Knight Rises and then celebrating his first wedding anniversary on Sunday.

"He always had a smile, always made you laugh. He had a little bit of comic in him," said Sullivan's uncle, Joe Loewenguth.

With files from CBC News