[cnn-photo-caption image=http://i2.cdn.turner.com/cnn/2009/images/07/08/goa.bomb.art.jpg caption="A GAO report cites lax security in federal buildings after investigators got bomb compenents past guards."]
WASHINGTON (CNN) - Plainclothes investigators sent to test security at federal buildings in four U.S. cities were successful in smuggling bomb components through guard posts at all 10 of the sites they visited, according to a government report.
The investigators then assembled the bombs in restrooms and freely entered numerous government offices while carrying the devices in briefcases, the report said.
The buildings contained offices of several federal lawmakers as well as agencies within the departments of State, Justice and Homeland Security, which is responsible for safeguarding federal office buildings.
CNN obtained the report late Tuesday, ahead of its expected release Wednesday at a hearing of the Senate Committee on Homeland Security and Governmental Affairs.
The Government Accountability Office, the investigative arm of Congress, conducted the tests to check on the effectiveness of the Federal Protective Service .The FPS protects federal buildings by having about 1,200 federal law enforcement officers oversee an army of 13,000 private security guards.
In a videotape obtained by CNN, a covert GAO inspector places a bag containing bomb components on an X-ray machine conveyor belt and then walks through a magnetometer at an unidentified federal building. Unlike some covert tests that use simulated explosives, the GAO used actual bomb components in the test and publicly available information "to identify a type of device that a terrorist could use" to damage a building.