"There's generally an event or a situation where the individual feels he has to intervene or somehow drastic action is called for. And then you see the horrible event that you saw last night," he said.
Hobfell said the Internet can be an important tool in fueling a person's assurance that their alternate reality is the correct one.
"You can become part of a cult or way of thinking through a chat room and develop a whole mindset with a group of people online. They spur each other on, they develop a common language," he said. "The Internet and games, that becomes the world they are living in."
There is also speculation about whether Holmes may have drawn inspiration from the storyline of the movie itself. His clothing and appearance are similar to the villain in "The Dark Knight Rises," Bane, who wears a gas mask, bulletproof vest and carries a gun. Others say it's impossible to know right now what factors drove the shooter.
Currently, nothing is known about whether Holmes had undergone psychiatric treatment or received a diagnosis of a mental health problem. But Torrey said he believes that the increasing numbers of shooting rampages – Jared Loughner's 2011 attack on Rep. Gabrielle Giffords, the shooting at Fort Hood in 2009, the massacre at Virginia Tech in 2007 – are largely the result of decreasing resources and funding for the mentally ill in state budgets throughout the U.S.
"This is just another tragedy of the many tragedies we're seeing like this. The sad thing is they are preventable if we treat these people," he said.
For continuing coverage on Tragedy in Colorado: Movie Theater Massacre, tune in to "World News," "20/20" and "Nightline."