By Kevin Anderson
BBC News Online Washington Correspondent
Richard Nixon left the White House in disgrace as the only president in US history to resign, and with the release of 500 hours of taped conversations covering the time of the Watergate break-in, researchers hope to find new clues to how much the president knew of the "third-rate burglary".
The tapes are of the first six months of his second term of office, covering not only the Watergate break-in but also his historic trip to China and the continuing war on Vietnam.
500 hours of tape have been released
Congress had once battled the president for release of the tapes, and now for the first time researchers and historians can record them to review them for new insights into the past.
But some questions will go unanswered as gaps remain on the tapes - gaps in key conversations that might have revealed how much Nixon knew about the break-in.
Nixon had the Secret Service install recording equipment in the White House, and the 1,000 tapes represent the first six months of 1972 as he turned his attention to winning re-election.
His political career had been a mixture of triumph and disappointment. After serving in Congress, he served as President Dwight Eisenhower's vice president.
He narrowly lost the 1960 presidential election to John Kennedy, and two years later, he lost the election for governor of California.
Nixon did not want to lose again.
The tapes include the Watergate "smoking gun" conversation
He was a fierce political competitor. When running for Congress in 1946, he printed his opponent's voting record on pink paper to suggest that he had Communist sympathies.
And as Nixon considered his re-election bid in 1972, he was looking for ways to beat his opponents.
In May of 1972, Arthur Bremer attempted to assassinate White House hopeful George Wallace.
The tapes reveal that Nixon wanted to pin the blame on supporters of Democrats George McGovern and Edward Kennedy, whom he might face in the November elections.
"Just say he (the shooter) was a supporter of McGovern and Kennedy," he said to HR "Bob" Haldeman, his chief of staff, and Charles Colson, then special counsel to the president.
"Now, just put that out!" Nixon said, his voice rising for emphasis. "Just say you have it on unmistakable evidence."
In the same conversation, Nixon gave new fodder for conspiracy theorists who question whether Lee Harvey Oswald was the only shooter involved in the assassination of President John Kennedy.
Referring to the report by the Warren Commission, "it was the greatest hoax that has ever been perpetuated," Nixon said. He did not elaborate why he questioned the report.
An 18 minute gap remains on the tape
The tapes also record a conversation between President Nixon and former Treasury Secretary John Connally who was in the car with President Kennedy when he was killed.
It contains graphic details of the shooting.
"I was lying... down on (wife) Nellie's lap like this to shield her head on top of me and I had my eyes open and I heard that bullet hit his head ... I knew he was dead," Mr Connally said.
President Nixon was also concerned that losses in Vietnam might threaten his re-election chances, and the frustrated president discussed using nuclear weapons with his National Security Advisor Henry Kissinger.
Mr Kissinger quickly dismissed the idea. "That, I think, would just be too much," he told the president.
"The nuclear bomb. Does that bother you?" he asked Mr Kissinger, adding, "I just want you to think big".
But the tapes also relate to more mundane topics such as his conversation with a Washington reporter about panda mating habits. As part of improved relations with the US, China gave two giant pandas to National Zoo in Washington.
There were great hopes that the panda pair would mate, but President Nixon explained a delay in the arrival of the pandas by saying they were learning to mate.
"The only way they learn how is to watch other pandas mate, you see, and so they're keeping them there a little while - these are younger ones - to sort of learn, you know, how it's done," he told the reporter, adding with a laugh that the reporter could not get back to covering more important subjects.
But no doubt researchers will be poring over the tapes to learn more about Watergate, the scandal that eventually led to Nixon's resignation.
Many questions remain about "who knew what when" with respect to Watergate, and some of those questions will remain.
The tapes include the so-called smoking gun conversation that was played during the Watergate investigation.
But a gap of 18 minutes and 30 seconds still remains, the tape going from the hiss and echoes of the long ago recorded conversations to a steady hum.