The paths that brought six men together in a Baghdad military clinic traced across the globe, from South America to rural Missouri, from the islands of Alaska to deepest Antarctica, before intersecting in a tragic shooting spree.

Authorities say Sgt. John M. Russell, who was nearing the end of his third tour in Iraq, was deeply angry at the military when he walked into the combat stress clinic at Camp Liberty on Monday and opened fire.

Two of the men who died devoted their careers to helping men like Russell: soldiers suffering from the stress of combat and repeated deployments to dangerous overseas war zones.

Keith Springle, a Navy commander who grew up swimming and fishing off the North Carolina coast, was in Iraq because it was his duty as a military psychologist. Dr. Matthew Houseal, a psychiatrist and major in the Army...