The FBI had consistently denied that inflammable tear gas had been used at Waco, and the Attorney General, Janet Reno, had endorsed their denial. But last week she disclosed new evidence that incendiary devices had been used and admitted the information had not been forthcoming from the FBI. The new tapes were not produced as evidence during earlier investigations into Waco. What is not clear is whether their existence was concealed.
With pressure mounting for a new investigation into the conduct of the assault on the compound, Ms Reno was expected to name a prominent judge or retired senator to head an independent inquiry.
The origins of the fire that ripped through the compound at Waco have been the subject of fierce controversy ever since the FBI assault on 19 April 1993. Many right-wing groups blame the FBI for deliberately starting the conflagration that destroyed the compound. The official version is that the cult leader, David Koresh, started the fire in a suicide pact.
Relatives of some victims are bringing a lawsuit for "wrongful death" against the federal authorities and the tapes came to light during preparation for the case, which opens in Waco next month. There is also evidence that the military Delta Force was present, though it has not been established whether it took part.
The Waco revelations revived the discord between Ms Reno and the head of the FBI, Lawrence Freeh. They were in open conflict during the investigation of the White House scandals, including alleged abuses of party funding and the Clintons' involvement in the Whitewater land deal.