Despite all the focus on chemical, nuclear and biological weapons during the coalition advance, there was a week between when the Republican Guard abandoned the Al-Tuwaitha Nuclear Research Center (30 kilometers south of Baghdad) and American marines showed up. Meanwhile, looters went over the place. It does not appear that the looters got into the "Location C" portion of the research center. Here is stored the 500 tons of unprocessed uranium and uranium dioxide, plus 1.8 tons of low-enriched uranium and radioactive isotopes that could be used for "dirty bombs." It turned out that there was a complex system of tunnels under the center that arms inspectors, after many visits, were unaware of.