This month’s shooting deaths of police in Baton Rouge, La., and Dallas by former servicemembers who saw combat in Iraq and Afghanistan comes as the Army is trying to better understand why up to 40 percent of troops return from war struggling with anger and aggression.

Police say rage may have driven Gavin Long, 29, who served five years in the Marine Corps, to kill three police Sunday and Micah Xavier Johnson, 25, a former Army reservist, to fatally shoot five officers on July 7.

Whether there is a link between their military service and the shootings is unknown. And military researchers have been studying the issue of anger for almost a decade.

Since 2007, a series of studies have shown 14 percent to 40 percent of troops surveyed after returning from war or while in the war zone report signs of anger such as kicking, smashing or throwing things, or threatening someone with physical violence. Anywhere from 4% to 18% were getting into fights.