NY Times :

A mob of gunmen went on a brazen daytime rampage through a predominantly Sunni Arab district of western Baghdad on Sunday, pulling people from their cars and homes and killing them in what officials and residents called a spasm of revenge by Shiite militias for the bombing of a Shiite mosque on Saturday. Hours later, two car bombs exploded beside a Shiite mosque in another Baghdad neighborhood in a deadly act of what appeared to be retaliation. While Baghdad has been ravaged by Sunni-Shiite bloodletting in recent months, even by recent standards the violence here on Sunday was frightening, delivered with impunity by gun-wielding vigilantes on the street...read on