24-year-old James Holmes, charged with the horrific massacre during a screening of the new Batman movie, dropped out of medical school just a month ago.
INSIDE EDITION spoke to a man who a man who knew him in Aurora, Colorado.
"This is a shock to everybody. He was someone who you would not even think twice when walking down the street. Very, very mellow," he said.
Hours after the shooting spree, James Holmes' father left his home in San Diego with a police escort to fly to Colorado to see his son.
He said nothing about his son or the tragedy, but a San Diego police officer read a statement from the family.
"Their hearts go out to the friends and family of those that were involved. And they are cooperating with law enforcement and they just ask for your patience, indulgence and respect at this time," said the family spokesperson.
When his mother, Arlene, was told of his arrest she reportedly said, "You have the right person."
Here's what else we've learned about the alleged shooter: He went to high school in San Diego and graduated in 2006. Some neighbors said that he was a quiet and nice. Other neighbors said that he was smart-alec and hard to get along with. His mother is a nurse and in June last year, he enrolled in the University of Colorado Medical School and was studying for his Ph.D in neurosciences. He was athletic, he played soccer in high school and joined the cross country team.
Kim Goff, a neighbor of the Holmes' told INSIDE EDITION, "I feel terrible for these victims. My feeling is, 'What happened?' This was this nice kid, grew up in a nice neighborhood. I don't know what happened."
One classmate said, "He watched people. I mean he was very quiet and just sat in the back, and watched people."
He graduated from the University of California at Riverside with a degree in neuroscience. He had an internship at the Salk Institute for Biological Studies in California.
Criminal profiler Pat Brown says Holmes is evidently a psychopath and she wouldn't be surprised if he had long history of mental problems.
"Nobody can commit a mass murder like this unless he's a psychopath. This is not a normal person who snapped. He was not healthy psychologically up until this particular day. This is a person who has always had problems with other people," said Brown.
Explosives experts on a cherry picker broke the window of his apartment in Aurora, where all the residents of the complex attend the University of Colorado. They tore out blinds to get a closer look at the booby trap bombs police said he placed inside.
Brown said, "Clearly this is somebody who's a little bit more sophisticated. Something must have gone wrong, where now he is angry at the world and this is his way of getting back at everybody."
Holmes is already being compared with other notorious mass killers—Eric Harris and Dylan Klebold, who killed 13 at Columbine High School just 13 miles from Aurora. Seung-Hui Cho, who killed 32 at Virginia Tech in 2007. And Jared Lee Loughner, who shot Arizona Congresswoman Gabby Giffords in a supermarket parking lot last year.
Now, another face has been added to a gallery of horrors.