Guys, let's put the political BS aside here...
Baghdad was for years the official, undisguised home address of Abu Nidal, then the most-wanted gangster in the world, who had been sentenced to death even by the PLO and had blown up airports in Vienna and Rome. Baghdad was the safe house for the man whose "operation" murdered Leon Klinghoffer.
In 1993, a certain Mr. Yasin helped mix the chemicals for the bomb at the World Trade Center and then skipped to Iraq, where he remained a guest of the state until the overthrow of Saddam.
In 2001, Saddam's regime was the only one in the region that openly celebrated the attacks on New York and Washington and described them as just the beginning of a larger revenge.
And it was after, and not before, the 9/11 attacks that Abu Mussab al-Zarqawi moved from Afghanistan to Baghdad and began to plan his now very open and lethal design for a holy and ethnic civil war.