(CNN) -- While officials have provided few details about the U.S. Army soldier accused of killing 16 Afghan men, women and children in a house-to-house shooting rampage in two villages, one psychiatrist speculated the incident may have stemmed from mental illness, but not necessarily post-traumatic stress disorder. "Post-traumatic stress disorder has a cluster of symptoms, and violence, or violence against, others is not usually considered part of that diagnosis," said Paul Newhouse, a professor of psychiatry at Vanderbilt University and a former Army psychiatrist. "So I think it's more likely that we're going to discover that there was some either psychotic illness or delusional condition or some evidence that this person was more seriously deranged or impaired than we would typically see in PTSD."
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Officials say the suspect was on his fourth deployment
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He suffered a traumatic brain injury in 2010 in Iraq but was cleared for duty
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Psychiatrist: It's unlikely the solder was suffering from post-traumatic stress disorder
He served three tours in @placeholder, but this was his first deployment to Afghanistan, Allen said.