From the same NYT story K-Lo cited:

A family of 13 was killed on the road leading to Falluja, about 12 miles northwest of Baghdad, because its members were from a tribe known to oppose Al Qaeda in Mesopotamia, witnesses said.
The family, including an elderly woman and two small boys, was dragged out of a minibus, lined up and shot. The bodies remained on the highway for hours because people were afraid they would be ambushed if they collected the dead, witnesses said.
The family was part of the Albu Farag tribe, which has made an alliance with the Anbar Salvation Council. The council has been trying to undermine the militants, and its leader, Abdul Satar Abu Risha, was himself the target of an assassination attempt on Monday when a suicide bomber drove into his home in Ramadi. He survived, but five of his guards were killed.
The attack on the Tarmiya outpost came as American troops moved into similar stations throughout Baghdad for the first time since the early months after the 2003 invasion. Monday’s attack underscored the inherent risks in the new strategy.
The Americans entered Tarmiya after the local police force collapsed in December, following a campaign of intimidation by Al Qaeda in Mesopotamia…