Mr. Santiago suffered from a documented major mental illness,  with psychosis and delusions.  We must step out of our normal world view and understand that someone with this illness does not see the world the same as someone without this major mental illness.  Of course, Mr. Santiago believed that his world view was real, even when it was not.  His decision to go to the FBI office had everything to do with being actively delusional and nothing to do with choosing the VA instead of the FBI.  It's possible that his mental illness was there before his National Guard experience.  We do not know his early mental health history.  

Santiago's actions are not an indictment of veterans or the mental health system.  He was delusional and believed his actions to be directed from some outside force...period.