The US National Archives has released grand-jury testimony given by former president Richard Nixon after the Watergate scandal forced him to resign.
Jurors asked about almost 19 missing minutes of a key conversation between Mr Nixon and his chief of staff.
The former president swore it was an accident that tapes had been erased, saying "I practically blew my stack."
The secret testimony was given under oath in June 1975 and released by order of a judge following a request by an historian.
The BBC reports the grand jury was collecting evidence to determine whether to issue criminal charges relating to the Watergate scandal.
The former president offered no clues as to what might have been discussed during the gap of 18 minutes and 30 seconds in recordings.
Watergate began with the arrest in June 1972 of five men for breaking into the Democratic National Congress offices at the Watergate complex in Washington DC.
Two years later, Mr Nixon was forced from the White House after it was revealed that he played a leading role in the cover-up from the beginning.
He resigned as president on 9 August 1974 and died on 22 April 1994.