OF all the many dangers facing the Iraqi people, perhaps the very greatest lurks in their own hearts. Foreign journalists regularly comment on the remarkable cheerfulness and stoicism of ordinary Iraqis who live their lives daily in the shadow of violent death. But as the sectarian violence increases, some men who were once proud to call themselves Iraqis, not Sunni or Shiite or Kurd, are being infected with poisonous hatred of each other. The barbarous massacre of 70 Sunnis in the northwestern border town of Tal Afar is an ominous development. Shiites carried out the murders in revenge for a truck bombing in a Shiite district of the town, which left 55 dead. Tal Afar is a place where Sunnis and Shiites once lived together in peace and intermarriages. It allegedly became an Al-Qaeda and insurgent base until two years ago when coalition and Iraqi forces completely cut off the town and moved in and arrested suspected terrorists.

The attack on the Shiite quarter was almost certainly perpetrated by killers from out of town, either Baathists or Al-Qaeda thugs. It was designed to provoke exactly the furious Shiite response that has occurred. Indeed the terrible retribution in which some Sunni men were dragged from their homes, many handcuffed, and executed on the streets, probably exceeded the wildest dreams of the insurgents. The fact that no Sunni gunmen attempted to stop the carnage almost certainly proves the complete innocence of Tal Afar’s Sunnis in Tuesday’s anti-Shiite crime. In a blood-soaked act of great stupidity, the furious Shiites therefore almost guaranteed that, in due time, more of their own community would die in further revenge attacks from those of Tal Afar’s Sunnis who had been radicalized by their own massacre.

There was however something even worse about this bloodletting: The Iraqi government has admitted that among the killers were Iraqi policemen. It is bad enough when — either through fear or complicity — policemen have stood by and done nothing while brutal crimes are committed, but for them to have participated in this reprehensible and thuggish behavior is too much. The authorities in Baghdad must move swiftly to detain, try and severely punish all who took part in the crime, especially the men who have been put in charge of maintaining peace.

In the capital, the authorities face an uphill struggle to convince ordinary Iraqis that the local cops are there to guard and protect them. In Tal Afar, a city of some 200,000 Iraqis of mainly Turkmen origin, the challenge ought to be easier. The 2,250 policemen in and around the town represent the Iraqi state and have all sworn to uphold the law and protect every citizen without fear or favor. It must be hoped that only a few renegade law officers took part in this wicked carnage. It must also be hoped that their colleagues are not only deeply ashamed of these crimes but determined that they should be punished. This was a disgusting crime, not just against Sunnis, not just against Iraqis, but also against humanity itself.