16 civilians were murdered by a U.S. soldier in a horrific house-to-house killing spree On the Western allied side, while not all hands were clean, civilians were murdered only on the initiative of maddened, drunk or brutal individuals, often seeking sex. What prompts men arbitrarily to kill? Even at home in civil society, the U.S. is prone to massacres carried out by maniacs -- invariably male -- often at schools and universities. Britain is not completely immune, as the Hungerford and Dunblane shootings showed. But armies are susceptible to special perils because they train young men to override our taboos against taking life, to become -- to put the matter bluntly -- professional killers. Most soldiers remain tightly disciplined and fully understand the gravity of pressing the triggers of deadly weapons. Nonetheless, in a theatre of war the risk is always there that an individual -- or more often small group of men -- will snap under stress, giving way to feral instincts. In March 2006, for instance, four American soldiers of the supposedly elite 101st Airborne Division raped and killed a 14-year-old girl at her home south of Baghdad, also murdering her parents and six-year-old sister. High alert: The Afghan Taliban has vowed revenge for the killings Correspondent Jim Frederick, who wrote Black Hearts, a devastating account of the killings, pointed a finger of blame at the men's battalion commander for failing to recognise that the ringleader of the murderers was losing his mind: 'In my opinion, he and