Some lingering questions and possible answers:
Q: What were the burglars after when they broke into the Democratic headquarters at the Watergate building on Friday night, June 17, 1972?
A: It's known the break-in was a follow-up to replace a faulty telephone bugging device installed during an earlier break-in. But why break into Democratic headquarters at all? The most obvious theory may be the right one: that Nixon simply wanted to keep tabs on the opposition.
There are other theories: that the burglars were trying to find, or plant, evidence linking the Democrats to left-wing radicals; that Nixon feared Democratic Party chairman Lawrence O'Brien had information about a loan from billionaire Howard Hughes to Nixon's brother, Donald; that the taps were to find out about a call-girl ring that served both the Democrats and the White House.
Q: Did Nixon send in the burglars?
A: None of Nixon's White House tapes so far made public reveals him saying anything that shows he had advance knowledge of the Watergate break-in.
But the tapes showed Nixon was aware of other illegal activities by subordinates. A year before Watergate, he is heard telling his chief of staff, HR "Bob" Haldeman, that he wanted Haldeman to steal a file on Vietnam from the Brookings Institution. "Break in and take it out," he directed. The order was never carried out. A former Nixon aide, Jeb Stuart Magruder, said in 2003 that he remembered listening in on the phone as Nixon gave the go-ahead for the Watergate bugging plan. Some historians reacted with scepticism.
Q: Why didn't Nixon destroy the tapes before they brought him down?
A: Nixon probably would have stayed president had the tapes not survived. Treasury Secretary John B Connally proposed burning them but lawyer Leonard Garment advised Nixon that the tapes could not lawfully be destroyed.
Also, Nixon was convinced he would never have to give them up. In his 1978 memoirs, he wrote that their destruction would have created an impression of guilt and they "were my best insurance" against another unfaithful aide like John Dean, who spilled the Watergate beans to investigators.
Q: Who caused a 18-and-a-half minute gap in one important tape?
A: The disclosure that one crucial tape a conversation three days after the break-in contained a noisy 18 1/2-minute buzz was enormously damaging. Nixon aide Alexander Haig blamed "a sinister force". Rose Mary Woods, Nixon's personal secretary, took some of the blame.
But a panel of experts who studied the damaged tape concluded Miss Woods could not have done the whole thing.
The experts found evidence of at least five, possibly as many as nine, deliberate erasures.