Documents gathered by lawyers for the families of Sept. 11 victims provide new evidence of extensive financial support for Al Qaeda and other extremist groups by members of the Saudi royal family, but the material may never find its way into court because of legal and diplomatic obstacles.

The case has put the Obama administration in the middle of a political and legal dispute, with the Justice Department siding with the Saudis in court last month in seeking to kill further legal action. Adding to the intrigue, classified American intelligence documents related to Saudi finances were leaked anonymously to lawyers for the families. The Justice Department had the lawyers’ copies destroyed and now wants to prevent a judge from even looking at the material.