By Joseph Ax NEW YORK (Reuters) - Suleiman Abu Ghaith, a son-in-law of Osama bin Laden, was found guilty of terrorism-related charges on Wednesday following a three-week trial that offered an unusually intimate portrait of al Qaeda's former leader in the days after the September 11, 2001 attacks. Abu Ghaith, 48, a Kuwait-born teacher, faces life in prison after a federal court jury in New York convicted him of conspiring to kill Americans, conspiring to provide material support for terrorists, and providing such support. Prosecutors had accused Abu Ghaith, one of the highest-profile bin Laden advisers to face trial in a U.S. civilian court since 2001, of acting as an al Qaeda mouthpiece, using videotapes of his inflammatory rhetoric to recruit new fighters. They also said Abu Ghaith knew in advance of an attempt to detonate a shoe bomb aboard an airplane by Briton Richard Reid in December 2001, citing in part an October 2001 video in which he warned Americans that the "storm of airplanes will not stop." Lawyers for Abu Ghaith said the prosecution was based on "ugly words and bad associations," rather than actual evidence that the defendant knew of or joined plots against Americans.