I could just link this as the Denial Quote of note, but the current article has an actual explanation.

The Americans' problems are compounded by the fact that the same Shiite-led Interior Ministry police forces they are training to protect Iraqis are widely suspected in the killings -- if not as the executioners, then as allies to the Shiite militias blamed for much of the bloodshed.

"No police allowed," a hand-painted banner declares in Adhamiyah, a middle-class quarter of homes and gardens behind high brick walls that is one of the largest Sunni districts in Baghdad. In clashes last month, Adhamiyah homeowners took up guns to fight off what they took to be Iraqi police, possibly backed by Shiite militias, trying to enter the barricaded neighborhood.

On Baghdad Patrol, a Vigilant Eye on Iraqi Police
U.S.-Trained Allies Are Often Suspects
By Ellen Knickmeyer
Washington Post Foreign Service
Monday, May 15, 2006; A01

BAGHDAD -- Second Lt. Will Shields started night patrol for his 2nd Platoon Delta Company with the Baghdad basics: a reminder to speed up instead of slow down if a bomb hits the convoy, and a heads-up on where to stash any victims of killings, sectarian and otherwise.

"We find any dead bodies, we've got three or four body bags," the 23-year-old Shields said. "Hopefully, that'll be enough."

The young troops in his platoon briefly grumbled good-naturedly about whose Humvee always gets stuck hauling the corpses they find of equally young Iraqi men -- stiffened, blood-streaked and open-mouthed. Pretty much every day, U.S. and Iraqi troops are picking up apparent victims of Sunni-Shiite violence on the streets of Baghdad.

Since Feb. 22, when the bombing of a Shiite Muslim shrine in Samarra pushed sectarian tensions in Iraq to a new plateau, the U.S. Army units have quietly moved back into some neighborhoods that U.S. commanders had just turned over, with fanfare, to Iraqi security forces. Iraqi leaders asked for the return of the American troops into parts of central Baghdad in March, fearing that efforts to build a stable government would fall apart if they were unable to rein in the Shiite-Sunni killings, said Col. Jeffrey Snow, commander of the 1st Brigade Combat Team of the 10th Mountain Division.

After fighting for nearly three years to put down an insurgency waged by Sunni Arabs, the Americans now are also dealing with a bloody Shiite-Sunni power struggle fought largely through intimidation and murder. Part civil war, with open battles in Baghdad's mixed southern neighborhood of Dora and the northern Sunni neighborhood of Adhamiyah, and part mob-style violence, with bodies being dumped out of cars that then speed away, the struggle plays out mostly beyond the view of U.S. soldiers.

Mystified Americans often are reduced to helping clear away the unidentified Iraqis left sprawled -- their tortured hands clutching the air or wired together behind their backs -- on curbs, sidewalks and garbage-strewn lots.

"It may be making a statement, and it may work for the Iraqi people, but we have a hell of a time figuring out what the statement is," Snow said.