In a strange footnote to history, Richard M. Nixon unwittingly testified on behalf of Deep Throat in a federal court trial in October 1980 -- six years after Nixon was forced to resign as president because of his involvement in the Watergate scandal.

Deep Throat was the confidential source who provided insider guidance crucial to The Washington Post's coverage of the scandal and the revelations that Nixon and his top aides covered up a massive campaign of political sabotage on behalf of his reelection efforts. On Tuesday, The Post confirmed that W. Mark Felt, the FBI's second-ranking official at the time of the 1972 break-in at the Democratic National Committee headquarters at the Watergate, was Deep Throat.

Six years after Nixon was driven from office, Felt and Edward S. Miller, formerly head of the FBI's domestic intelligence division, were charged with illegally authorizing government agents in 1972 and 1973 to break into homes without warrants in search of anti-Vietnam War bombing suspects from the radical Weather Underground organization.

Nixon, then a private citizen, testified that he believed that at the time the FBI director and his deputies had direct authorization from the president to order break-ins in the interest of national security.

Much of Nixon's testimony focused on his efforts to end the Vietnam War while his administration was confronted with violent antiwar activism. "It was quite different than what it is today," Nixon testified. At one point, a woman seated among the spectators cried out, "War criminal!"

Felt was subsequently convicted and fined $5,000. But five months later, President Ronald Reagan pardoned Felt on the grounds that he had "acted on high principle" to bring an end to the terrorism threatening the nation.

-- Eric Pianin

Former president Richard M. Nixon spoke to reporters before testifying in a 1980 trial.