Grad school dropout's horrific attack came out of nowhere The 24-year-old man who police say walked into a Colorado movie theater and sprayed patrons with gunfire is a grad school dropout who grew up in San Diego and had only one known brush with the law - a traffic ticket last year. Police say James Egan Holmes burst into the crowded Century 16 movie theaters in Aurora, Colo., where midnight showings of the Batman movie "The Dark Knight Returns" were airing in five theaters and opened fire with three guns, killing at least 12 and injuring scores. What snapped in the neuroscience student's brain is unclear. An Aurora man who told The Associated Press he had a beer Tuesday with a stranger he later realized was Holmes said they talked about Peyton Manning, the Denver Broncos' new quarterback. "We just talked about football," said Jackie Mitchell, a furniture mover. He had a backpack and geeky classes and seemed like a real intelligent guy and I figured he was one of the college students. Mitchell also said Holmes seemed smart, with a "swagger." Holmes, who stands 6-foot-3, graduated from San Diego's Westview High School in 2006, Poway Unified School District confirmed to Fox News. A gifted student, he studied neuroscience at nearby University of California-Riverside, where he graduated in 2010. Anthony Mai, a 16-year-old who grew up next door to Holmes, described Holmes as a "solitary" person who largely kept to himself but his behavior was nothing out of the ordinary. He felt a little bit concealed, but it wasn't too much. It was alright" he said. This is just a feeling in my gut, but I felt like he had something, like he was being picked on or something. His father, Tom Mai, a retired electrical engineer, said Holmes was quiet. I said hello to him once in a while. He seemed to be a shy guy," he told reporters. He said the Holmes have lived at the San Diego home about 10 years and they were a "very, very nice family." Holmes mother is a nurse. The suspect also has a younger sister. Last fall, Holmes began graduate work in the same discipline at University of Colorado School of Medicine in Denver until last month, according to school spokeswoman Jackie Montgomery. She did not know why he dropped out. A college syllabus shows classes Holmes would have taken included topics such as diverse as substance abuse, schizophrenia, depression and other disorders. Holmes described himself last year in an apartment rental application as "quiet and easy going," the Denver Post reports. Holmes, who is in police custody and is reportedly not cooperating with authorities, appears to have meticulously planned the horrific attack, booby-trapping his apartment near the Aurora, Colo., with what police described as "incendiary and chemical devices" equipped with sophisticated tripwires. At the cinema, he entered through a fire door he'd previously left open and then set off some sort of explosive before opening fire with multiple guns, including an AR-15 assault rifle, a shotgun and at least one .40-caliber Glock handgun. Holmes, who was dressed in black and wearing a protective vest, was arrested by his car outside the movie theater minutes after the attack. Holmes did not resist cops and reportedly told them his apartment - just four miles from the theater and within view of Children's Hospital, where some of his victims were taken - was rigged to kill. Police say the attack is not tied to terrorism and have thus far have provided no motive. Holmes' only known brush with authorities was a speeding ticket issued last October. Federal law enforcement sources told USA Today Holmes "was not on anybody's radar."