Several mental health experts have spoken about this over the past few days.  There is no statistical link between PTSD and family violence.  To link the soldier's PTSD diagnosis with his murdering family members is unfair to others suffering from PTSD because it perpetuates the stigma that mental illness makes people dangerous.  On the contrary, the fact is that people with mental illness are at higher risk of harming themselves, and those with PTSD typically withdraw rather than act out.

Since those with PTSD are at a higher risk of suicide, that part of the soldier's actions could possibly be explained by his mental illness.  His decision to kill his wife, his daughter and his mother as well can't.