HELMAND, AFGHANISTAN — Jason Armas, a U.S. Marine Corps captain, scrolled through the photographs of four bearded Afghan men believed to be responsible for the assassination of Marine 1st Lt. Scott J. Fleming.

A few days earlier, on the eve of Afghanistan’s parliamentary elections, Taliban insurgents shot the 24 year-old Marietta, Ga., man through the neck, killing him instantly. Fleming’s comrades from the 3rd Battalion, 3rd Marine Regiment were intent on capturing the Taliban who had killed the young platoon leader.