A review of classified documents by former members of the Sept. 11 commission shows that the panel made repeated and detailed requests to the Central Intelligence Agency in 2003 and 2004 for documents and other information about the interrogation of operatives of Al Qaeda, and were told by a top C.I.A. official that the agency had "produced or made available for review" everything that had been requested. 

The review was conducted earlier this month after the disclosure that in November 2005, the C.I.A. destroyed videotapes documenting the interrogations of two Qaeda operatives. 

A seven-page memorandum prepared by Philip D. Zelikow, the panel's former executive director, concluded that "further investigation is needed" to determine whether the C.I.A.'s withholding of the tapes from the commission violated federal law. 

The two chairmen of the commission, Lee H. Hamilton and Thomas H. Kean, said their reading of the report had convinced them that the agency had made a conscious decision to impede the Sept. 11 commission's inquiry. 

Mr. Kean said the panel would provide the memorandum to the federal prosecutors and congressional investigators who are trying to determine whether the destruction of the tapes or withholding them from the courts and the commission was improper. 

9/11 Panel Study Finds That CIA Withheld Tapes