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WASHINGTON, Dec 19 (Reuters) - Mark Felt, the mysterious "Deep Throat" source who helped Washington Post reporters Bob Woodward and Carl Bernstein crack the Watergate scandal that brought down President Richard Nixon, has died at age 95.
Felt suffered from congestive heart failure but the exact cause of his death at home on Thursday was not immediately known, said the Press Democrat newspaper in Santa Rosa, California, 55 miles (90 km) north of San Francisco.
In its report on Felt's death, the New York Times called him "the most famous anonymous source in American history."
Felt, the No. 2 official at the FBI when the Watergate case broke, kept his role in the story a secret for 30 years. Only in 2005, at age 91, was his part made public in an article in Vanity Fair magazine written by Felt's family lawyer.
"I'm the guy they used to call Deep Throat," Felt told attorney John O'Connor.
For years, people had speculated and argued about the identity of "Deep Throat," whose name was derived from the title of a popular pornographic movie.
Vanity Fair scooped Woodward and Bernstein, who had promised not to reveal the name of the star source of their 1974 stories until after his death. But within a day of Felt's unveiling, Woodward wrote of his relationship with Felt.
Woodward said he turned to Felt after he and Bernstein wrote about the break-in at the offices of the Democratic National Committee at the Watergate complex in Washington.
"This was the moment when a source or friend in the investigative agencies of government is invaluable," Woodward wrote in the Post. "I called Felt at the FBI ... It would be our first talk about Watergate."
Woodward said Felt told him the Watergate case was going to "heat up." He abruptly hung up but then started to provide guidance on the story, Woodward said.
Following a complicated routine, Felt and Woodward would arrange to meet in an underground garage, with "Deep Throat" corroborating information the Post reporters had gleaned from other sources and outlining a government conspiracy.
"Felt believed he was protecting the bureau by finding a way, clandestine as it was, to push some of the information from the FBI interviews and files out to the public, to help build public and political pressure to make Nixon and his people answerable," Woodward wrote.
"He had nothing but contempt for the Nixon White House and their efforts to manipulate the bureau for political reasons."
Reporting by the Post and other news organizations on the White House's involvement in the Watergate break-in and other political "dirty tricks" forced Nixon's resignation in 1974.
More than 30 officials would ultimately plead guilty or be convicted, including Attorney General John Mitchell, who served 19 months for conspiracy, obstruction of justice and perjury.
Felt repeatedly denied he was "Deep Throat," even though his position at the FBI made him an obvious candidate, and Nixon himself suspected Felt of leaking to the media.
A character patterned on Felt showed up in the book and movie "All The President's Men," an account by Bernstein and Woodward of their Watergate reporting. Played by Hal Holbrooke, the "Deep Throat" character was seen in the shadows.
This portrayal was true to life, Woodward wrote, because Felt insisted on anonymity and was concerned that phone calls might be tapped.
Last month, Woodward and Bernstein visited Felt in Santa Rosa. It was Bernstein's first meeting with the famous source, who dealt only with Woodward during the Watergate days.
Born on Aug. 17, 1913 in Twin Falls, Idaho, Felt came to Washington as a Capitol Hill staff member and later worked at the Federal Trade Commission before joining the FBI in 1942.
He served in the bureau's espionage section during World War Two and later worked in various field offices and oversaw some of the FBI's early investigations into organized crime.
Felt was appointed deputy associate director, the No. 3 job at the FBI, in 1971, and was disappointed when Nixon named L. Patrick Gray to head the agency after the death of its longtime chief, J. Edgar Hoover, in 1972.
Felt was convicted in 1980 of authorizing illegal break-ins at five homes in New York and New Jersey as part of the FBI's pursuit of the radical Weather Underground group. He was fined $5,000 and then pardoned by President Ronald Reagan in 1981.
Felt and his wife Audrey, who died in 1984, had two children. (Writing by Deborah Zabarenko; Additional reporting by Dean Goodman in Los Angeles; Editing by John O'Callaghan)