SAN JOSE, Calif. (KGO) -- Investigators are still searching for a motive in Wednesday's shooting massacre in Thousand Oaks, Calif.
Ian David Long, 28, has been identified as the suspected gunman who killed 12 people. Long was found dead at the scene and authorities believe he shot himself.
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The U.S. Marine Corps confirmed Long served from 2008 to 2013, and was deployed to Afghanistan from November 16, 2010, to June 14, 2011.
Long is part of the so-called "new generation of veterans" who are fighting in an environment experts say is much different than previous wars.
"There's no front line. These wars have been fought primarily through improvised explosive devices," clinical psychologist Dr. Elena Klaw told ABC7 News. "So that means that every man, woman or child that you see could be an enemy."
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Dr. Klaw is also the director of Veterans Embracing Transition at San Jose State University. She explained the combat experienced in the Iraq or Afghanistan wars could impact a veteran's transition to civilian life.
"You can't tell who's an enemy, and who's a combatant and who isn't," she continued. "So that required an enormous amount of what we call hyper vigilance."
"Veterans have told me that the hardest part of their service has been coming home," Klaw said.
Long's neighbors told the media they suspect he suffered from Post Traumatic Stress Disorder, or PTSD.
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On Thursday, Ventura County Sheriff Geoff Dean explained one scenario which involved a crisis intervention team and mental health specialists responding to Long's Newbury Park home.
Dean explained Long was cleared after specialists determined he wasn't qualified to be taken under 5150, referencing the California law code for the temporary involuntary psychiatric commitment of individuals who present a danger to themselves or others due to signs of mental illness.
"My guess is he clearly wasn't deemed to be of imminent risk of harm to self or to others," Klaw explained. "Despite needing mental health treatment."
ABC7 News reached out to the VA Palo Alto Health Care System. A spokesperson confirms Long was not enrolled in VA health care at any time.
Klaw told ABC7 News, "I think the problem is that we have disenfranchised educators, mental health professionals, nurses, social workers. People who provide all levels of care, and have ignored the essential nature of providing a safety net for all vulnerable people that will continue to be at risk of violence."
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Thousand Oaks shooter was part of 'new generation of veterans,' psychologist says
THOUSAND OAKS MASS SHOOTING