Fort Hood gunman 'was unstable'
Unstable mental health may be the underlying cause of a soldier's fatal shooting rampage at Fort Hood in Texas this week, investigators said.
But they also believe an argument with another service member probably preceded the attack.
Specialist Ivan Lopez turned his gun on himself after killing three people and wounding 16 others on Wednesday at the nation's largest army post.
It is the same military base where more than a dozen people were fatally shot by a soldier in 2009.
Lt Gen Mark Milley, Fort Hood's senior officer, said Lopez's psychological issues may be the "fundamental, underlying cause" of the attack.
Lopez had been undergoing treatment for depression and anxiety while being evaluated for post-traumatic stress disorder.
Lt Gen Milley also said Lopez was probably involved in an argument before the shooting.