Mr. Moussaoui’s sensational allegations have drawn attention in part because far more credible figures, including some members of the national 9/11 Commission, believe the Saudi role in the attacks has never been adequately examined. More broadly, the episode has drawn new attention to Saudi Arabia’s longtime policy of using its oil wealth to try to shape foreign battlefields, currently by backing militants in Syria and Libya, and the reactionary religious ideology that underlies its society.

Throughout the 1980s, Saudi Arabia and the United States were partners in bankrolling the mujahedeen, hailed as freedom fighters by President Ronald Reagan, who were battling the Soviet military in Afghanistan.

Some of those fighters coalesced under the leadership of Bin Laden in 1988 to form Al Qaeda, which soon put the Saudi state on its list of enemies along with the United States. While private Saudi support for Bin Laden’s organization continued to flow, experts who study the kingdom said they doubted it would have come from top officials like those named by Mr. Moussaoui, at least after 1994.

The investigation of the Sept. 11 attacks, in which 15 of the 19 hijackers were Saudi, would most likely have turned up such high-level support if it existed, said F. Gregory Gause III, a professor at the Bush School of Government and Public Service at Texas A & M University, who studies Saudi Arabia.