Fourth Infantry Division battalion commander Lt. Col. Steve Russell said a preliminary inquiry into the shooting has been completed and a report sent to military headquarters in Baghdad.

Russell said the report indicated that a heavy caliber machine gun was used in the attack in which a man woman and child were killed.

"I think it is likely coalition forces were involved given the fact that a heavy-caliber machine gun was used," Russell said.

A survivor told Iraqi police that American troops opened fire on the victims’ car as it passed a convoy.

None of the U.S. troops in the area had reported the shooting as required by military regulations.

The 4th Infantry Division has said none of its soldiers was involved in the shooting.

Russell said Tuesday that the main supply road around Tikrit where the incident happened is used by a number of units, which means it’s possible that if the incident occurred as described, that troops from a unit other than the 4th Infantry Division were involved.