Wilburn Russell spoke with reporters Tuesday in front of the northern Texas house owned by his son, Army Sergeant. John M. Russell.
The elder Russell says his son was six weeks away from completing his third tour in Iraq before Monday's shootings.
He says his son was treated poorly at the military stress center and had e-mailed his wife calling two recent days the worst in his life.
Wilburn Russell says his son felt like "his life was over" and that he had "lived for the military."
He says he hopes "we find he snapped because of the pressure. He wasn't a mean person."
The shooting occurred at Camp Liberty, a sprawling US base on the western edge of Baghdad near the city's international airport and adjacent to another facility where President Barack Obama visited last month.
A brief US statement said the soldier "suspected of being involved with the shooting" was in custody but gave no further details. It was unclear what provoked the attack.
"Anytime we lose one of our own, it affects us all," US spokesman Col. John Robinson said. "Our hearts go out to the families and friends of all the service members involved in this terrible tragedy."
Attacks on officers and sergeants, known as fraggings, were not uncommon during the Vietnam war as morale in the ranks sank. However, such attacks are believed to be rare in the wars in Iraq and Afghanistan.
In 2003, Army Sgt. Hasan Akbar was sentenced to death for killing two officers in Kuwait just before the US-led invasion of Iraq of 2003.
In June 2005, an Army captain and lieutenant were killed when an anti-personnel mine detonated in the window of their room at the US base in Tikrit. A National Guard sergeant was acquitted in the blast.
Additionally, there have been several incidents recently when gunmen dressed as Iraqi soldiers have opened fire on American troops, including an attack in the northern city of Mosul on May 2 in which two soldiers and the gunman were killed.
