According to Bill Gertz's book, "Breakdown", Sudan wanted to be taken off the U.S. terrorist list back in 1998 and bin laden was living there at the time and they offered to arrest him and let the U.S. have him with his known terrorist ties and funding, but the Clinton admin. didn't seem interested and instead, bombed what turned out to be a pharmaceutical company building.
Gerts'z book is about how the FBI and CIA not only made mistakes up to 9/11, but also the Clinton admin. and even as far back as the Carter admin. established laws and rules that hampered their info. seeking procedures. Not to mention hiring cronies to run departments in the CIA and FBI that had no experience in those roles and it showed.
Even the new FBI guy Mueller was more worried about being criticized for profiling than tracking down people who seem to fit the mold of the known terrorist factions.