From A High-Risk Nuclear Stakeout:
...Interviews with current and former government officials and intelligence agents and outside experts in Washington, Europe and the Middle East reveal a lengthy pattern of watching and waiting when it came to Khan and his illicit network.
The trail dated back more than 20 years as Khan went from a secretive procurer of technology for Pakistan's atomic weapons program, which he headed, to history's biggest independent seller of nuclear weapons equipment and expertise.
For most of those years, Khan's primary customers were Iran and North Korea.
The Bush administration wasn't alone in it's failure to stop Kahn's nuke ring. But even after declaring Iran and North Korea as part of the "Axis of Evil", and lying to the world about non-existent WMD in Iraq, Kahn continued to ply his trade.
BushCo knew this stuff. Yet they threw a red herring at us, because chasing Kahn and his connections wasn't politically "convenient". Even today, we're not being told the full scope of Kahn's illegal activities. Still, having received a summary slap on the wrist by the Pakistani government, Kahn is a free man, with the full sanction and knowledge of the Bush administration.