CIA contract security officers who responded to the terrorist attacks on the U.S. ambassador in Benghazi, Libya, last year were told by the CIA to sign nondisclosure agreements just before a memorial ceremony at the CIA’s headquarters in Langley, Virginia, this past May, a congressional source told CNN.

The source says this was disclosed by the contractors during closed-door testimony on Capitol Hill this week, and it seems to contradict information sent by CIA Director John Brennan to the House Intelligence Committee investigating the events in Benghazi.

The CIA has repeatedly denied reports by CNN that the CIA has tried to prevent its personnel from talking to members of Congress investigating the September 2012 Benghazi attacks.