INDIANAPOLIS — Decades before Donald Trump fired off tweets about FBI leaks, a senior intelligence official huddled with a Washington Post reporter in a dark, damp parking garage and fed him bread crumbs along a trail that would end in a president’s resignation.

W. Mark Felt was the second in command at the FBI at the time it was investigating President Richard Nixon and his men in the months following a June 1972 break-in at the Democratic National Committee headquarters in the Watergate business complex. The cover-up of a host of legally questionable activities would eventually result in Nixon’s ouster in August 1974.

During that time Felt “wrote the book” on leaking, San Francisco-based attorney John O’Connor said.

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O'Connor, a 70-year-old native of Indianapolis' north side, outed Felt to the world as Watergate's "Deep Throat" in a July 2005 article for Vanity Fair. Now, Felt's biography has become a major motion picture.

Mark Felt: The Man Who Brought Down the White House is set to hit Indianapolis area theaters Friday and stars Liam Neeson in the title role.

Felt "knew, deep down inside, that what he did was right,” O’Connor told IndyStar.

'Deep Throat' theories

Post reporters Bob Woodward and Carl Bernstein introduced readers to "Deep Throat" in the 1974 novel All the President's Men, which details their investigation from the day of the break-in through January 1974, months before Nixon’s resignation. They described the informant as a source with an "extremely sensitive" position within the executive branch with whom Woodward conducted secret meetings in the middle of the night. Hal Holbrook portrayed "Deep Throat" in the 1976 film.

For years, theories circulated about who the informant could have been. The reporters — and the Post — swore to protect his identity, and O'Connor thinks Felt would have been happy never to have revealed his secret.

"Had Woodward not featured this character in the book ... no one ever would’ve known that he leaked," O'Connor said. "He would’ve gone to the grave with that."

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O’Connor said he had known since the 1970s that Felt was the man behind "Deep Throat" — “that was a real obsession of mine,” he said — but he didn’t get the chance to confirm it until he met Felt’s grandson by happenstance at a dinner party O’Connor and his wife threw for their daughter and some friends in 2002.

O’Connor was telling stories of his own father’s days with the FBI when one of his daughter’s friends spoke up.

“I was just telling some funny stories when the young fellow across the table from me said, ‘Well, maybe your father knew my grandfather. He was in the FBI. … His name’s Mark Felt,’” O’Connor remembered. “My jaw dropped.”

Outed in Vanity Fair

Through the grandson he met Felt. It took three years for O’Connor to persuade him — and a publication — that it was time to bring “Deep Throat” out of the shadows. Although O’Connor said Felt knew he did the right thing, he was afraid of the repercussions it would have for the Bureau.

"He always felt that some of the power of the FBI was its reputation, was of the conduct of its agents,” O’Connor said. "He knew that this culture that he was in charge of — he was in charge of the culture for many years — that it was a very strict, strict, no-nonsense culture, that those guys may not understand.”

Working as the family’s attorney, O’Connor was finally able to convince Vanity Fair that their story was credible and that Felt was ready to come forward. The story published in May 2005 and was featured in the magazine's July issue.

After the Vanity Fair article, Woodward, Bernstein and the Post confirmed Felt's identity. Two months later, in July 2005, Woodward published The Secret Man, which detailed the relationship between the top FBI official and the investigative reporter.

"Secret Man was not especially kind to him," O'Connor said. "All the President's Men was much kinder to ‘Deep Throat’ and in my view much more truthful because there was no need to take gratuitous shots at the FBI."

When he came out, Felt was criticized by some, including those at the FBI, for being the agent who undermined the Nixon presidency. But there were others, like O’Connor, who lauded him for being a hero who stood up for what was right.

"He was not trying to get the president," O'Connor said. "He was not trying to get (FBI Acting Director L. Patrick) Gray. He was just trying to do his job, but they kept making the mistake of trying to stop him. And unfortunately he’s not a guy that would just shut up and go along with it.

"There’s no doubt he was taking big chances.”

Speaking out put Felt’s inner turmoil to rest.

"He was in a prison that he made himself," O’Connor said, "and I think we helped him get out of prison."

Coming out of the shadows lifted the weight off Felt’s shoulders in his final years, O’Connor said. Felt died Dec. 18, 2008, at age 95, just over three years after the big reveal. O’Connor thinks the new film is a perfect ending to the story that started with All the President’s Men.

The film depicts the internal hunt among Washington officials to determine the identity of the well-placed whistleblower and shows the tensions between the executive and judicial branches.

Government leaks

The story, though decades old, feels relevant in 2017’s political climate. Just months ago, the president publicly accused former FBI Director James Comey of leaking classified information to reporters. O’Connor said he believes there will always be a place for leakers in the American governmental system.

That's not to say the White House should be a sieve. O’Connor said he thinks there should probably be more punitive action taken against leakers who divulge information that could damage national security — something Felt was careful never to do. But ethical whistleblowers, O’Connor said, are the people you hope will stand up in risky situations.

"If you leak for purposes of upholding ethical standards, of making sure that your government or corporation does not break a law or do something unethical, I think that’s really the power of our democracy," O'Connor said. "I think that’s where democratic systems heal themselves."

Follow Holly Hays on Twitter: @hollyvhays