Fort Hood gunman 'was unstable'

Unstable mental health may be the “fundamental, underlying cause” of a soldier’s shooting rampage at a US military base, though an argument with another service member probably preceded the attack, according to investigators.

Specialist Ivan Lopez turned his gun on himself after killing three people and wounding 16 others on Wednesday at the sprawling Texas military base of Fort Hood, where more than a dozen people were killed by a soldier in 2009.