Enough details have emerged from survivors and military personnel to conclude that in the town of Haditha last November, members of the 3rd Battalion, 1st Marine Regiment perpetrated a massacre. The killings may have been in retaliation for the death of a Marine lance corporal, but this was not the work of soldiers gone berserk. The targets (children from 3 to 14, an old man in a wheelchair, taxi passengers), the hours-long duration of killings, the number of Marines involved, the careful mop-up–all amount to willful, targeted brutality designed to send a message to Iraqis. As Representative John Murtha has pointed out, the patently false story floated afterward, blaming the killings on roadside bombs, and Marine payoffs to survivors imply a cover-up that may extend far up the chain of command.

What matters about Haditha? After all, Iraq is a place where civilians die every day. Many of them die as a result of insurgent car bombs, or at the hands of Sunni or Shiite militias. Many thousands of others died in US air attacks early in the war (as civilians did recently in airstrikes in another US war zone, Kandahar).

Even in this context there remains a distinctly sickening horror in close-up systematic killing of civilians that’s at odds with the declared US mission in Iraq and is repugnant to our national ideals. Even under intense battlefield conditions, troops can instigate atrocities, or they can resist them. In the My Lai massacre, in 1968, Hugh Thompson Jr., an American helicopter pilot, saved many lives by putting himself between the guns of Charlie Company and the villagers whom those behind the guns–led by their officers–were wantonly killing. A generation of future US military officers were taught the details of the My Lai massacre as a particular lesson: What makes war crimes is criminal leadership. Whatever the responsibility of the unit commanders in Haditha, it is George W. Bush as Commander in Chief who has sent the clear message that human rights abuses and violations of international law are justified in the “war on terror.”

That the Marines institutionally covered up Haditha until Time magazine raised questions with the Corps suggests that the moral damage from the Iraq War is broader than a single debased unit. That is what so powerfully motivates Murtha, a Marine and Vietnam veteran. Another Marine, Senator John Warner, is promising hearings, but his Armed Services Committee’s toothless investigation of Abu Ghraib offers scant hope of serious inquiry. As with My Lai a generation ago, it is participants in the Haditha killings or cover-up–some haunted by what they saw or heard about–who are bringing details to the press.

What happened in Haditha and how it was covered up is only half the story. The rest is yet to unfold: whether Haditha kindles a long-overdue reckoning with the moral catastrophe of this war or the shock gets defused by low-level Congressional inquiries; whether Haditha turns out to have been the low point of the US military venture in Iraq or a foreshadowing of worse to come. What we need is not the “picture of what happened” promised by the White House but a full-scale investigation both of the massacre in Haditha and of the climate of impunity that allowed it to happen and to be ignored for so long.