People who knew the Colorado shooting suspect James Holmes said he was a quiet, academically-oriented man.
Holmes, who formerly lived in San Diego, was arrested in a Denver suburb early Friday morning on suspicion for fatally shooting 12 people and wounding several others in a movie theater premiere of “The Dark Knight Rises."
Holmes attended UC Riverside, where he graduated with highest honors in 2010, according to Chancellor Timothy P. White.
Neighbors and friends said Holmes went by "Jimmy."
Sumit Shah, 24, said he went to Westview High School in Rancho Penasquitos with Holmes, where they graduated in 2006.
“I knew him pretty well, we were friendly,” said Shah. “He was pretty shy, but once he got comfortable with you, he was the funniest, smartest guy… He always had something witty to say.”
Shah said he was shocked to learn what happened.
“I don’t even understand how,” he said. “The guy I knew in high school, I don’t understand how that could be the same guy…He was shy and little quiet, but he was never aggressive or mean. He always had really good grades. He seemed pretty normal.”
Shah and Holmes sat next to each other in an AP U.S. History class. Shah said they would eat lunch together and Holmes would sometimes join in lunch hour football games.
"He was pretty quiet, but when he got comfortable, he was pretty talkative, he said. "He was mostly a nice guy."
Shah called the situation "tragic."
"Its a horrible thing to happen. I couldn't imagine anybody I know would be capable of that sort of thing," said Shah. "Its kind of weird to see him go from the guy I knew to somebody who would kill 12 people and counting."
Get more coverage in our special section: The "Dark Knight" Massacre
A 16-year-old neighbor Anthony Mai said he knew Holmes his whole life. He said he cannot believe that Holmes performed such an act.
“James was happy and smiling,” said Mai.
Holmes also had trouble finding a job a few years ago, Mai said.
Holmes played soccer and run cross country from when he was a student at Westview High School.
Alex Van Horne played Junior Varsity soccer with Holmes at Mesa Verde Middle School.
"He was never one of those people who you looked at and thought there was something inside that needed to come out," Van Horne said. "I don't remember him standing out."
He also said Holmes wasn't someone who stood out.
"There's people you see in high school that you worry about sometimes, but he wasn't one of those ... He always seemed fine," said Van Horne.
Holmes' uncle, who shares his name, lives in Carmel, Calif. and said that he was blown away when he heard the news. He said his nephew was a "nerd" and "unassuming kid."
Neighbor Marjorie Aguliar said her son know Holmes when he lived in San Diego, and also said he was “quiet.” Another neighbor Ilana Aroson said Holmes used to swim with the fellow neighborhood kids in her backyard pool, but she hasn’t seen him in many years.
"He was a nice kid and grew up in a nice neighborhood," said neighbor Kim Goff to NBC 7 San Diego. "Whenever I spoke to his mother she was very proud of him."
Goff also said that Holmes' family has lived in San Diego for more than 15 years.
"I feel so bad for his parents," said Goff. "They're just such nice people."
San Diego County Deputy District Attorney Wendy Patrick spoke about traditional red flag warning signs that will be part of the investigation in this case.
“Gosh this guy was a Ph.D. student. Lots of people would look at that and say this doesn’t seem to be the kind of person who would target a theater full of people… on the opening night of a blockbuster film,” Patrick said.
Patrick, who teaches Business ethics at San Diego State University and is co-author of “Reading People,” said there are a number of things investigators will be looking at.
“People who knew him, how he spent his time, what he talked about,” she said. “Some people talk about fantasies of doing stuff like this....You want to look at and talk to people who really knew him personally to get a fuller picture of who he was.”
Holmes is currently in custody in Colorado. Police said his apartment was "booby-trapped" with explosives that appeared "very sophisticated." The explosives were disarmed by bomb squad experts Saturday.
The man did not want to be identified, but he did tell NBC 7 that Holmes helped mentor him in science and described Holmes as “really intelligent, a good person, and a nice gentleman.”
NBC 7 also spoke with several former Westview High School students Saturday. They didn’t want to speak on camera but did say that they remembered Holmes walking through the hallways of Westview but they said they never saw Holmes speaking with anyone.
Others who played soccer with Holmes for a short time at Westview described the Colorado shooting suspect as "nice,” “intelligent,” and easy-going back in high school.
Keep up to date on breaking news: Download our improved iPhone app, follow us on Twitter @nbcsandiego, fan us on Facebook, sign up for our breaking news e-mail alerts or text SDBREAKING to 622339 to receive text messages for local breaking news. (For more info, text HELP. To end, text STOP. Message and data rates may apply.)