The HSCA conducted public hearings, but also took a great deal of testimony which remained secret until the passage of the JFK Records Act and the wholesale release of HSCA files (though in some cases with redactions). Ten boxes of "security classified" testimony was taken, much of it from CIA employees. One of these boxes is still withheld because it consists of depositions from the Martin Luther King, Jr. investigation. The contents of the other 9 boxes are all reproduced herein.

Only the first two depositions, both of them primarily concerned with the much-debated "Mexico City tapes," are from the early days of the HSCA when Richard Sprague was Chief Counsel. The remainder of the depositions were taken starting more than a year later. They are presented here in chronological order. Among the topics discussed in them are the CIA's pre-assassination knowledge of Oswald, its post-assassination investigative activities, and the treatment of Yuri Nosenko, the Soviet defector who claimed to have reviewed Oswald's file and who was kept locked in solitary confinement for 3 years by the CIA.