SAN DIEGO -- The alleged gunman in the deadly "Dark Knight" movie theater shooting had trouble finding work before he returned to school to study neuroscience in Colorado, a San Diego neighbor said Friday.

James Holmes, 24, who graduated from Westview High School in San Diego in 2006, could not find work after graduating from UC Riverside in 2010 with a bachelor's in neuroscience, said Tom Mai, a retired electrical engineer who lives in the Rancho Penasquitos neighborhood where Holmes grew up.

Holmes, who was arrested after the shooting Friday in suburban Denver, was described by law enforcement sources as a loner. He was a student at the University of Colorado Denver/Anschutz Medical Campus, but the school said he was in the process of withdrawing from the graduate program in neuroscience.

A former high school classmate, Keith Goodwin, 24, now a Columbia Law School student, said he had a couple of conversations with Holmes during an Advanced Placement European history class at Westview. He called Holmes a “generally pleasant guy.”

“James was certainly not someone I would have ever imagined shooting somebody,” Goodwin said.

Andrew Bustamante attended Mesa Verde Middle School and Westview High School with Holmes. He remembered a conversation in which Holmes said he was particularly interested in weapons, gas masks and going into battle, but Bustamante didn't give the comment much thought at the time.

"He was super nice and very sweet. He loved playing video games," Bustamante said.

Bustamante said that when he heard Holmes was accused of the shootings in Colorado, it shocking but not surprising.

Tori Burton, 24, a fellow with the National Institutes of Health, said Holmes was part of Westview's cross-country team for at least one year.

“He was very quiet,” she said. “He was a nice guy when you did occasionally talk to him. But he was definitely more introverted.”

Dan Kim, a 23-year-old student at UC San Diego, called the suspect a "super nice kid," "kinda quiet"  and "really smart."

Kim said Holmes took multiple AP classes and had an academically inclined circle of about five to 10 friends. 

"He didn't seem like a troublemaker at all," Kim said. "He just seemed like he wanted to get in and out, and go to college."

Holmes' last known address in California was at the University Iowa Gardens Apartments less than a mile from UC Riverside. Maintenance worker Jose Torres, 45, said he remembered Holmes as a quiet person who kept mostly to himself.

"He didn't talk too much," Torres said. “Friendly? No."

Professors at UC Riverside recalled Holmes as an honor student and could provide no clues that would indicate he was capable the violent attack that left 12 people dead and dozens of others injured, Chancellor Timothy White said.

White said professors who knew Holmes expressed shock and disbelief about the movie theater shooting at the premiere of "The Dark Knight Rises" in Aurora, Colo. He said that many on campus were still trying to understand happened.

White said counseling is being offered to faculty and staff who may have known Holmes.

"He was an honor student, so academically, he was at the top of the top," White said. Holmes graduated from the university with a bachelor's degree in neuroscience in 2010.

Mai said he remembers Holmes as a very shy, well-mannered young man who was heavily involved in their local church.

"He seemed to be a normal kid. I don't know what triggered it. This makes me very sad," Mai said.

Holmes was taken into custody early Friday in the parking lot outside the Century 16 movie theater after the post-midnight attack in Aurora, Colo. He allegedly entered the theater through an exit door about half an hour into a screening of the new Batman movie"The Dark Knight Rises."

At least 12 people were killed in the attack. Witnesses described a chaotic scene, telling television reporters that they were overcome by noxious gas unleashed by the suspect just before he started shooting, and that they had to decide between staying on the ground, helping wounded victims or running away before the gunman was able to reload his weapon.

Survivors said they were forced to run past bodies in the aisles. The attack was smoky and surreal, witnesses reported, as moviegoers, some wearing their own costumes, slowly realized that bullets were flying from the weapon of the man in body armor whose face was hidden by a gas mask.

"There were bullet [casings] just falling on my head. They were burning my forehead,” Jennifer Seeger told reporters afterward. “Every few seconds it was just: Boom, boom, boom," she said. "He would reload and shoot and anyone who would try to leave would just get killed."

The shooter was armed with a rifle, a shotgun and two handguns, police said. Cellphone videos from the scene show panicked moviegoers running -- some screaming -- and others with blood visible.