DENVER – James Eagen Holmes came from a well-tended San Diego enclave of two-story homes with red-tiled roofs, where neighbors recall him as a clean-cut, studious young man of sparing words.

Tall and dark-haired, he stared clear-eyed at the camera in a 2004 high school yearbook snapshot, wearing a white junior varsity soccer uniform — No. 16. The son of a nurse, Arlene, and a software company manager, Robert, James Holmes was a brilliant science scholar in college.

The biggest mystery surrounding the 24-year-old doctoral student was why he would have pulled on a gas mask and shot dozens of people early Friday in a suburban Denver movie theater, as police allege.

In the age of widespread social media, no trace of Holmes could be found on Facebook, LinkedIn, MySpace, Twitter or anywhere on the Web. Either he never engaged or he scrubbed his trail.

A longtime neighbor in San Diego, where Holmes grew up, remembers only a "shy guy ... a loner" from a churchgoing family. In addition to playing soccer at Westview High School, he ran cross country.

The bookish demeanor concealed an unspooling life. Holmes struggled to find work after graduating with highest honors in spring 2010 with a neuroscience degree from the University of California, Riverside, said the neighbor, retired electrical engineer Tom Mai.

Holmes enrolled last year in a neuroscience Ph.D. program at the University of Colorado-Denver but was in the process of withdrawing, said school officials, who didn't provide a reason. The school later said in a statement that he left the program in June 2012.

As part of the advanced program in Denver, a James Holmes had been listed as making a presentation in May about Micro DNA Biomarkers in a class named "Biological Basis of Psychiatric and Neurological Disorders."

In academic achievement, "he was at the top of the top," recalled Riverside Chancellor Timothy P. White.

Holmes concentrated his study on "how we all behave," White added. "It's ironic and sad."

From a distance, Holmes' life appears unblemished, a young man with unlimited potential. There are no indications he had problems with police.

Somehow, the acclaimed student and quiet neighbor reached a point where he painted his hair red, called himself "The Joker," the green-haired villain from the Batman movies, according to New York City Police Commissioner Ray Kelly, who said he had been briefed on the matter.

Authorities say Holmes arrived at the theater dressed in black, outfitted in a gas mask, ballistic helmet, vest and leggings, black tactical gloves and protectors on his throat and groin. He was armed with an assault-style rifle, a shotgun and Glock handgun.

Police said he started his attack by tossing two gas canisters into the theater, where he had bought a ticket for the midnight showing of "The Dark Knight Rises," the new Batman movie.

A federal law enforcement official, speaking on condition of anonymity because of the ongoing probe into the rampage, said Holmes bought four guns from retailers in the past two months.

Holmes bought his first Glock pistol in Aurora, Colo., on May 22. Six days later, he picked up a Remington shotgun in Denver. About two weeks later, he bought a .223 caliber Smith & Wesson rifle in Thornton, Colo., and then a second Glock in Denver on July 6 — 13 days before the shooting, the official said.

A high-volume drum magazine was attached to the rifle, an assault weapon, the official said. Aurora Police Chief Dan Oates said that a 100-round drum magazine for the rifle was recovered from the scene.

"I'm told by experts that with that drum magazine, he could have gotten off 50 to 60 rounds, even if it was semiautomatic, within one minute," Oates said at a news conference. "And as far as we know, it was a pretty rapid pace of fire in that theater."

Julie Adams, whose son played junior varsity soccer with Holmes, said her son remembered little about the suspect, which was unusual for the tight-knit team.

"I don't think many of the kids (teammates) knew him. He was kind of a loner," she said.

Jackie Mitchell, a furniture mover who lives several blocks from the suspect's apartment building in Colorado, said he had drinks with Holmes at a bar on Tuesday night, though he showed no sign of distress or violence.

After Holmes approached him, "we just talked about football. He had a backpack and geeky glasses and seemed like a real intelligent guy, and I figured he was one of the college students," Mitchell said.

When Mitchell saw Holmes' photo after the shooting, "the hair stood up on my back," he said. "I know this guy."

Holmes is not talking to police and has asked for a lawyer, according to a law enforcement official briefed on the investigation. The official spoke on condition of anonymity to discuss the case. Police found jars of chemicals in Holmes' booby-trapped apartment with wires nearby, the law enforcement official said.

When he surrendered meekly in the movie house parking lot, Holmes told authorities what he'd done at his residence in the Denver suburb of Aurora, the third most populous city in Colorado.

"Our hearts go out to those who were involved in this tragedy and to the families and friends of those involved," Holmes' family said in a statement Friday. "We ask that the media respect our privacy during this difficult time."

San Diego Superior Court spokeswoman Karen Dalton said there were no records found under his name, not even for a traffic ticket. Riverside County prosecutors also have no criminal record for him, said John Hall, a spokesman for the district attorney's office. The only mark on his record in Aurora was a speeding summons from October, Oates said.

On Friday morning, police escorted the suspect's father from the family's San Diego home. The mother stayed inside, receiving visitors who came to offer support.

San Diego police spokeswoman Lt. Andra Brown spoke to reporters in the driveway of the Holmes' home, on behalf of the family.

"As you can understand, the Holmes family is very upset about all of this," she said. "It's a tragic event and it's taken everyone by surprise."