3) It was just two years after the Gulf War. In terms of enemies wishing America harm, Iraq was on the top of the list.
4) Mohammed Salameh had many communications with Iraq in a crucial, early stage of the plot. Between June 10 and July 9, 1992, when his phone service was cut off, he made 46 calls to Iraq (see GX 824, US vs. Salameh et. al.)
But one can do more than just suspect Iraq's role, which, of course, is important. It can be demonstrated to a high standard, perhaps even "beyond a reasonable doubt," that Iraq was behind the attack. That demonstration revolves around the identity of the mastermind, Ramzi Yousef, without whom the bomb could not have been built.
He entered the U.S. on an Iraqi passport as Ramzi Yousef. He fled the U.S. the night of the Trade Center bombing on a Pakistani passport in the name of Abdul Basit Karim.
In December 1992, Yousef went to the Pakistani consulate in New York with xerox copies of pages from Karim's 1984 and 1988 passports. Yousef claimed to be Karim and said he had lost his passport and needed a new one to return home.
The consulate did not like the documentation, because there were no original documents, but still gave Yousef a temporary passport, which he used to flee the U.S.