WASHINGTON — U.S. archivists on Wednesday revealed one of the last great secrets of the Watergate investigation – the backbone of a long sealed report used by prosecutor Leon Jaworski to send Congress the evidence that led to the impeachment of President Richard Nixon.

The release of the 1974 impeachment referral came after a former member of Nixon’s defense team and three prominent legal analysts filed separate lawsuits seeking its release from grand jury secrecy rules. The legal analysts argued the report could offer a precedent and guide for special counsel Robert Mueller as his office addresses its present-day challenge on whether, and if so, how to make public findings from its investigation into Russia interference in the 2016 election, including any that directly involve President Donald Trump.

The legal specialists said they and Watergate veterans sought the release of the Jaworski report after more than four decades of secrecy because of the historic parallels they see to the current probe and the report’s potential to serve as a counterexample to the independent counsel Ken Starr’s report seeking president Bill Clinton’s impeachment.

The 453-page Starr report, written in 1998, deepened partisan divisions when its graphic detail and legal conclusions about Clinton’s affair with Monica Lewinsky were immediately made public by House Republicans, who suffered an electoral backlash.

By contrast, the reputation of Jaworski’s report has fared far better, even as its bare-bones form remained a mystery. The Jaworski report is known colloquially known as the “Sirica road map,” for then-Chief U.S. District Judge John J. Sirica, who approved its creation and transmission to lawmakers

“There were no comments, no interpretations and not a word or phrase of accusatory nature. The ‘Road Map’ was simply that – a series of guideposts if the House Judiciary Committee wished to follow them,” the late Jaworski wrote in his 1976 memoir, “The Right and the Power: The Prosecution of Watergate.”

Sirica’s modern-day successor, Chief U.S. District Judge Beryl A. Howell of the District, on Oct. 11 ordered the disclosure of his report – with limited redactions – in response to petitions by California author and former Nixon deputy Watergate defense counsel Geoffrey Shepard and by Brookings Institution senior fellow Benjamin Wittes; Jack Goldsmith, a Harvard law professor who led the Justice Department’s Office of Legal Counsel under president George W. Bush; and Stephen Bates, a Las Vegas professor who co-wrote the Starr report with now-Supreme Court Justice Brett M. Kavanaugh and other members of Starr’s team.

In a statement Deana El-Mallawany, counsel for Protect Democracy, which represented the Wittes group, said, “The Road Map is a critical historical precedent for ensuring that the facts uncovered in Special Counsel Mueller’s investigation become public and serve as the basis for whatever accountability is necessary. Our democracy depends on it.”

The road map consists of a two-page summary, followed by 53 numbered statements, supported by 97 documents including interviews and tapes, according to information that the National Archives and Records Administration turned over to Howell.

While much of the report’s substance – including evidence of the Nixon campaign’s funding of the break-in of Democratic National Committee headquarters and the president’s role in the subsequent coverup – has long been public, its structure and potential to serve as a template for others remained under seal.

Bates said as a Starr prosecutor in 1997, he learned that despite the potential for the “road map” to present a legal model for future investigations, such as Mueller’s it was not publicly available when he asked the National Archives for a copy to study.

“It is one of the only precedents of a report that has had to go through that kind of process [under grand jury secrecy rules] to get to the House for consideration as grounds for impeachment,” Bates said in an interview. “If Mueller could say, ‘We have structured this report the way Leon Jaworski did in 1974, and Judge Sirica approved it,’ that might be persuasive in this case.”

Jaworski needed Sirica’s approval to send materials to Congress because they were covered under federal grand jury secrecy rules under a process overseen by the judge.

Jaworski faced a problem similar to one that may confront Mueller today: he had relevant evidence but not, he concluded, the constitutional authority to indict a sitting president. Congress had the authority to impeach Nixon, but not the evidence. In the end, the House committee sought access to evidence gathered by prosecutors, the grand jury adopted the road map, and Sirica and the U.S. Circuit Court of Appeals of the District of Columbia authorized its transmittal under seal.