Despite repeated reports of shootings of Iraqi civilians by Blackwater and other U.S. private security contractors, the incidents were "rarely" the subjects of full investigations, current and former State Department officials tell the Blotter on ABCNews.com. "We get almost weekly reports of such shootings, but it is close to impossible to go the crime scene and interview witnesses," said one current State Department official formerly based in Baghdad. The contractors are responsible for filing incident reports, the officials said, but the State Department could do little to follow up. Blotter: Contractor Rules in Iraq: Fire Only ‘Aimed Shots’ "To conduct a forensic investigation and go talk to witnesses where people can go to 10 different hospitals is nearly impossible in a war zone," the official said. Another official told ABCNews.com that the standard practice was for the contractor to be quickly moved out of the country. "They would just disappear, often within hours," said one former official who dealt directly with Blackwater and other contractors. In the most recent case involving as many as 20 civilians allegedly killed by Blackwater security guards, State Department spokesperson Sean McCormack says a full investigation is now underway by the State Department’s Bureau of Diplomatic Security. Officials said they want to know how many, if any, bullet holes there are in the Blackwater vehicles, to confirm the Blackwater guards’ version of events that they were fired upon. Blackwater says its employees "heroically defended" the U.S. officials they were assigned to protect. Do you have a tip for Brian Ross and the Investigative Team?