On a cloudy day in early November, the last of conservative writer Jerome Corsi’s six marathon interviews with the office of special counsel Robert S. Mueller III was about to begin. Sitting in a building in Southwest Washington, three prosecutors assigned to his case opened with a lecture.

For more than two months, they had been chasing tantalizing leads offered by Corsi, an associate of Trump confidant Roger Stone who had told them that the longtime GOP operative sought a back channel to WikiLeaks during the 2016 campaign.

They had dispatched FBI agents around the country to interview potential witnesses, expending valuable government money and precious time — only to find themselves unable to untangle Corsi’s assertions that Stone knew in advance that WikiLeaks would be releasing emails stolen from the account of John Podesta, Hillary Clinton’s campaign chairman.

“No lies, hunches, wishes,” prosecutor Aaron Zelinsky lectured Corsi that day as they sat in a windowless conference room, according to notes taken by Corsi’s lawyer, David Gray. “Hopes do not equal facts. Don’t tell us what you think we want to hear.”

The Yale-educated former Supreme Court clerk pleaded with Corsi: It was “vitally important” that Corsi provide the “truth only,” Zelinsky said.

The trio of top prosecutors had spent weeks coaxing, cajoling and admonishing the conspiracy theorist as they pressed him to stick to facts and not reconstruct stories. At times, they had debated the nature of memory itself.

Once again that day, however, Corsi struggled to answer clearly questions about Stone and WikiLeaks — closing the door on an exhausting final chapter of Mueller’s nearly two-year hunt to determine whether anyone in Trump’s world had coordinated with Russia.

The investigation took the special counsel’s team down several meandering paths, propelled by discoveries of unusual interactions between Trump associates and Russians. Trump campaign chairman Paul Manafort had shared internal information with an employee assessed by the FBI to have Russian intelligence ties. Foreign policy adviser George Papadopoulos was tipped off that the Russians had thousands of Clinton’s emails. Donald Trump Jr. met with a Russian lawyer who he hoped would offer damaging information about Clinton.

[Mueller’s report paints a portrait of a campaign intrigued by Russian overtures]

In the end, Mueller’s final report, a redacted version of which was released by Attorney General William P. Barr on Thursday, laid out new details about the Russian effort to influence the 2016 campaign through social media and the hacking of Democratic emails, and it offered a rich portrait of Trump’s efforts as president to undermine the investigation and mislead the public.

The 448-page report also revealed the outcome of the long endeavor to determine the relationship between Trump associates and Russia: some unanswered mysteries, a lot of dead ends and, ultimately, a conclusionthat the contacts they found did not establish a criminal conspiracy.

Stone has not been charged with serving as a conduit to WikiLeaks, which disseminated material stolen by Russians.

Instead, he was indicted in January for lying to Congress about his efforts to reach out to WikiLeaks. He has pleaded not guilty and has vehemently denied having any knowledge of what WikiLeaks held and the group’s exact plans. Stone has also denounced Corsi’s account as lies.

Corsi announced in November that he had rejected a deal to plead guilty to false statements and accused the special counsel’s office of trying to bully him into lying. He has not been charged with any crime.

A reconstruction of the laborious effort by Mueller’s team to determine whether the Trump campaign conspired with Russia shows why it was often a maddeningly difficult task.

Their witnesses were not ideal. A few key players, prosecutors would contend, lied in interviews. Many were loyal to the president and echoed his rhetoric that Mueller’s team was acting in bad faith. Some used encrypted applications with disappearing messages that could not be reviewed. Others were overseas, unreachable to American investigators.

In some cases, their statements were only loosely tethered to the facts.

This account is based on interviews with people who interacted with Mueller’s team, court documents and new details laid out in the special counsel’s report. A spokesman for the special counsel’s office declined to comment.

It was the first item in the order that Deputy Attorney General Rod J. Rosenstein issued in May 2017 when he appointed Mueller as special counsel.

As part of his charge, Mueller would take over a preexisting FBI investigation into “any links and/or coordination between the Russian government and individuals associated with the campaign of President Donald Trump.”

The inquiry had begun in late July 2016 after the Australian government contacted the FBI about Papadopoulos. Over drinks at a bar in London, the young Trump aide had confided to an Australian diplomat that the Russian government had thousands of Clinton emails that could damage her candidacy.

By the time Mueller was appointed, the FBI had interviewed Papadopoulos and, according to him, tried unsuccessfully to get him to travel to London and surreptitiously record a conversation with Joseph Mifsud, a Maltese professor who told him about the Clinton emails. In a 2017 interview with a British newspaper, Mifsud denied knowledge of the emails.

The FBI had also obtained a secret court order allowing them to monitor the communications of former Trump adviser Carter Page, who had traveled to Moscow during the heat of the campaign and interacted there with a Russian government official.

The work came against the backdrop of the publication of a research dossier prepared by a former British intelligence agent and funded by Clinton’s campaign, which claimed that Trump had engaged in a knowing conspiracy with Russia, which Trump dismissed as false.

The special counsel moved quickly on several fronts.

Weeks after Mueller was appointed, the FBI sent a search warrant to Google, scooping up Trump attorney Michael Cohen’s Gmail messages dating back to January 2016, court records show. His emails began to help investigators uncover the extent of his efforts to develop a Trump Tower project in Moscow — an attempt that persisted through much of the campaign, even as Trump publicly denied he had business ties in Russia, court filings show.

[‘We will be in Moscow’: The story of Trump’s 30-year quest to expand his brand to Russia]

By July, Mueller’s team was delving into Trump Jr.’s meeting the previous summer with Russian lawyer Natalia Veselnitskaya, which had also been attended by Trump’s son-in-law Jared Kushner and Manafort.

They started with a potentially neutral witness: the interpreter, interviewing him just four days after the New York Times broke the news of the meeting, according to the report.

Russian-born Anatoli Samochornov described to investigators what unfolded in the 20-minute meeting: Veselnitskaya raised the topic of Democratic donors who she alleged had broken Russian law. One of her associates then brought up a U.S. sanctions law against Russia and a ban on American adoptions of Russian children that the Kremlin had imposed in retaliation. Trump Jr. said there was little his father could do to address the issue, but said it could be revisited if Trump were elected.

In November 2017, prosecutors interviewed Ike Kaveladze, an employee of Aras Agalarov, the Russian billionaire who had hosted Trump’s Miss Universe pageant in 2013 in Moscow and requested the meeting through his son.

“They asked very targeted questions,” said Kaveladze, who had attended the meeting as the Agalarov representative. “I realized they had significant knowledge of the topic.”

Mueller’s team interviewed everyone who attended the meeting except Veselnitskaya, who is in Russia, and Trump Jr., who declined to participate voluntarily, they wrote. (It is unclear whether prosecutors attempted to subpoena the president’s son.)

The picture that was emerging was one of a campaign that was eager for Russia’s help at the same time the Kremlin had been working to elect Trump.

As 2017 stretched on, former national security adviser Michael Flynn pleaded guilty to lying to the FBI about his communications with the Russian ambassador during the transition. Papadopoulos pleaded guilty to lying about his contacts with Mifsud and two Russians.

By July 2018, Mueller had charged 25 Russians with participating in two plots to influence the White House race.

But the special counsel still had not resolved whether Russia coordinated with Trump associates.

In September last year, Mueller’s team got a break. Manafort, who had been a central figure in the investigation from the start, agreed to plead guilty to financial crimes and failing to register as a foreign lobbyist for work he had conducted in Ukraine before leading the Trump campaign.

At last, prosecutors had access to a key member of Trump’s inner campaign circle who also had deep connections in Russia, including a business relationship with Oleg Deripaska, a billionaire with close ties to Russian President Vladi­mir Putin.

Manafort’s deputy, Rick Gates, told prosecutors that, as soon as Manafort joined the campaign, he had asked Gates to prepare memos describing his elevated new role for Deripaska and three leading Ukrainian politicians. Emails show Manafort tried to get a message to Deripaska to offer him private briefings about Trump’s effort. Manafort told investigators he never gave Deripaska such briefings.

Manafort’s liaison to the Russian aluminum magnate was his own longtime Russian employee, Konstantin Kilimnik, who the FBI had assessed had ties to Russian intelligence, according to the special counsel.

The report said Manafort also provided campaign polling data to Kilimnik, described to him a strategy to win the election for Trump by contesting traditionally Democratic-leaning Midwestern states and discussed with him a pro-Russian peace plan for Ukraine, a top foreign policy goal of the Kremlin. Manafort would later say he understood Trump’s sign-off, if elected, would be necessary to advance the plan.

Manafort’s cooperation meant prosecutors finally had a firsthand witness who could explain whether there was ever a suggestion of a trade-off: Russian assistance in the campaign in exchange for a Trump administration that supported pro-Russian policies.

On Sept. 11, 2018, Manafort sat for the first of 11 interviews with investigators. He also appeared twice before the grand jury.

But, prosecutors alleged, he did not tell them everything he knew. A federal judge agreed, ruling in February that Manafort had lied intentionally to prosecutors, particularly about his interactions with Kilimnik.

“It’s part of a pattern of requiring the Office of Special Counsel to pull teeth — withholding facts if he can get away with it,” U.S. District Court Judge Amy Berman Jackson said during a February hearing.

In an email to The Washington Post last week, Kilimnik denied he had Russian intelligence ties and said he had not shared the polling information with anyone else. He said he had “absolutely . . . zero” to do with Russian interference.

Meanwhile, several prosecutors on Mueller’s team were pursuing another intriguing subject: Stone, a decades-old friend of Trump who had worked briefly for the celebrity mogul’s campaign in 2015 and then continued to informally advise him.

[Trump’s night-owl calls to Roger Stone in 2016 draw scrutiny in Mueller probe]

During the campaign, Stone egged on WikiLeaks as the London-based group leaked materials prosecutors say were provided by Russian operatives to help elect Trump. Starting in early August 2016, Stone began braggingpublicly that he had a way to communicate with Wiki­Leaks founder Julian Assange.

On Aug. 21, 2016 — six weeks before WikiLeaks published emails stolen from Podesta — Stone tweeted, “Trust me, it will soon the Podesta’s time in the barrel.”

The seemingly prescient and imperfectly phrased tweet did not mention WikiLeaks. But it led to suspicions by Podesta and others that Stone had been aware of WikiLeaks’ plans in advance.

For months, Mueller’s team sought to understand whether Stone shared information about WikiLeaks’ activities with the campaign, uncovering numerous examples of Trump’s deep interest in the Clinton emails.

At one point, during a drive to LaGuardia Airport, Trump told senior campaign official Gates that “more releases of damaging information would be coming,” Gates later told prosecutors.

Some in Trump’s orbit appeared to view Stone as having a hand in WikiLeaks’ activities. One person affiliated with a Trump campaign aide sent Stone a text message just after WikiLeaks published Podesta’s emails on Oct. 7. “Well done,” read the message, according to Stone’s eventual indictment, which did not identify the sender.

[Roger Stone was in close contact with Trump campaign about WikiLeaks, indictment shows]

After the election, Stone vociferously and repeatedly denied that he had been in contact with Assange or had any heads-up about WikiLeaks’ plans. He said that he never discussed Wiki­Leaks with Trump and that his claims during the campaign were just boasts and exaggerations.

Likewise, in written answers prepared by his attorneys, Trump told prosecutors he did “not recall discussing WikiLeaks” with Stone or being aware of Stone discussing the subject with others on his campaign, according to the report.

In September 2017, Stone testified to the House Intelligence Committee that his public hints about WikiLeaks were based on vague tips he’d been given by a New York City radio host and comedian named Randy Credico, whom he described as an “intermediary” and “mutual friend” of Assange.

Credico has denied serving as a back channel for Stone. He said he didn’t become acquainted with Assange until the WikiLeaks founder appeared on his radio show on Aug. 25, 2016. Stone began talking publicly about having a line to WikiLeaks weeks earlier.

Did Stone have another source? Prosecutors wanted to find out.

They brought Credico — along with his small white therapy dog Bianca — to Washington to testify before the grand jury. They interviewed Kristin Davis, a close Stone friend once known as the “Manhattan Madam” because she used to run a prostitution business catering to wealthy New Yorkers. They issued a subpoena to Stone’s business assistant and held him in contempt of court when he refused to testify.

[How an ex-madam, a political trickster and a toddler got tangled up in the Russia investigation]

They then turned their attention to Corsi, a conservative author who had emailed with Stone about WikiLeaks during the campaign.

Corsi, 72, had at one point worked in financial services, but more recently had become a popular writer on the fringe right. He wrote a book in 2004 accusing former secretary of state John F. Kerry of lying about his Vietnam service and then became a leading proponent of the false theory that President Barack Obama was not born in the United States, a topic over which he bonded with Trump.

On Aug. 28, 2018, two FBI agents banged on the door of Corsi’s New Jersey home, a grand jury subpoena in hand — kicking off a byzantine turn in the investigation.

After convening with Gray, a New Jersey attorney who had done legal work for his wife’s cleaning business, Corsi decided he would cooperate with prosecutors. He agreed to turn over his computers and passwords to his social media accounts and to sit for voluntary interviews.

But Corsi’s first meeting in September with prosecutors Zelinksy, Andrew Goldstein and Jeannie Rhee went quickly awry, Gray said in an interview with The Post.

Asked if he’d had anything to do with WikiLeaks during the campaign, Corsi issued a blanket denial. He claimed that he had told Stone during the campaign that trying to contact Assange was a bad idea that could subject them both to investigation, according to a draft court filing.

That wasn’t accurate.

By then, prosecutors had obtained emails showing that Corsi was in constant conversation with his friends and contacts, including Stone, throughout the final months of the campaign, speculating about Assange’s next moves, according to Gray.

On July 25, 2016 — a few days after WikiLeaks upset the Democratic National Convention by publishing internal Democratic Party emails — Stone emailed Corsi and asked him to get to Assange and find out what else the WikiLeaks founder held, according to a draft plea agreement Corsi released.

Corsi forwarded Stone’s note to Ted Malloch, an American author living in London who hoped to land a job with Trump and was eager to curry favor with his campaign, according to the draft filing.

According to the report, Malloch told prosecutors he never tried to reach Assange, who was living at the Ecuadoran Embassy. He declined to comment.

Eight days later, Corsi sent Stone an email hinting he had managed to pick up new intelligence on Assange: “Word is friend in embassy plans 2 more dumps.” He predicted one of WikiLeaks’ publications would come in October and referenced Podesta, according to the draft filing: “Time to let more than Podesta to be exposed as in bed w enemy if they are not ready to drop HRC.”

[Corsi provided early alert to Stone about WikiLeaks release, according to draft special counsel document]

Corsi has said he was never in direct or indirect contact with Assange. He said he was exaggerating his knowledge to Stone.

“I’m convinced my memory is correct that I didn’t have a source that connected me to Assange,” he told The Post in November. “I really don’t think so.”

But prosecutors used his initial assertion that he declined Stone’s request to seek information from WikiLeaks as a cudgel, saying he could be charged with a crime for lying, Corsi described in a book he wrote about the experience called “Silent No More” that was published in December.

They pressed him to explain: Did he ever reach Assange? Did he tell Stone in advance that WikiLeaks had Podesta’s emails? Did he and Stone help WikiLeaks time the releases for maximum impact?

Gray said that he believed Corsi was trying to be honest, but he acknowledged his client’s answers were not always clear or consistent.

He said he decided to share details from Corsi’s sessions with prosecutors — including reading to The Postfrom contemporaneous notes — to try to help the public better understand how the clash between the special counsel’s office and witnesses like Corsi frustrated and extended the investigation.

Corsi, he noted, had sold thousands of books and built a fan base by cherry-picking facts to craft a desired narrative. For Corsi, this wasn’t lying, but salesmanship, picking “truthful facts woven in a way that you don’t have to worry about the things that are inconsistent,” Gray said.

The deeply fact-based prosecutors struggled to make sense of the conspiracy theorist and his evolving testimony.

“It’s their biggest nightmare,” Gray said. “The supposed best of the best were just frankly dumbfounded by the whole situation.”

Over sessions in September and October, Corsi offered information that appeared enticing but sketchy.

Corsi claimed he had figured out on his own in early August 2016 that WikiLeaks had Podesta’s emails. According to the report, Corsi told Malloch in August or September that Wiki­Leaks would be releasing Podesta’s emails and then the Trump campaign would be” in the driver’s seat.”

Corsi also told prosecutors he alerted Stone that Podesta’s emails were coming and believed Stone’s “barrel” tweet was based on his information, Corsi has said.

He claimed he and Stone had then crafted a “cover story” after the tweet to avoid tipping people off to their information — a research memo Corsi submitted to Stone with information about John and his brother Tony Podesta’s business ties to Russia.

Stone told Congress that conversations he’d had with Corsi about the memo were the basis for his tweet, even though the memo was dated Aug. 31, 2016 — 10 days after he posted his message on Twitter about Podesta.

Gray said prosecutors appeared skeptical of Corsi’s claim that he had merely divined on his own that WikiLeaks would be releasing Podesta’s emails after determining that they were not included in the cache of the Democratic Party emails the group released in July. (Podesta, after all, did not work for the DNC, and his emails were not kept on the party committee’s servers.)

Over and over, they asked Corsi who had told him WikiLeaks held Podesta’s emails and whether he’d communicated with Assange. At one meeting, Gray said Corsi seemed to concede another person might have “planted a seed” in his mind about what WikiLeaks held. Then he said that “maybe he heard it from somewhere,” Gray said.

“His answer had morphed a bit. It was concerning to me, and it was concerning to the prosecutors,” he said.

In his book, Corsi insisted the prosecutors confused and rattled him with their repetitive questioning. At one point, he said he told the trio: “It frustrates me that I can’t remember . . . Sometimes I can’t tell if I remembered or invented.’”

Corsi told The Post in an interview last week: “I did not go in to lie or deceive them.”

“I told them from the beginning that I couldn’t remember my 2016 conversations with the kind of precision they were going to demand,” he said, adding: “I’m not a human tape recorder.”

The group spent long hours in a windowless conference room, with the three prosecutors and half a dozen FBI agents arrayed on one side of the table and Gray and Corsi on the other.

At one point, Gray recalled that his eyes wandered to a whiteboard that covered one wall of the room. It appeared to have been only recently erased from an earlier meeting, and he could just barely make out what had been written there previously:

“Ukraine” it said faintly, underlined three times, an apparent reference to Manafort’s interviews, which were underway during that period. Beneath that were dollar figures tallying into the tens of millions.

Among Corsi’s claims to prosecutors, according to Corsi’s book: that Stone had given him advance notice on Oct. 7, 2016, that The Post would be publishing a video in which Trump could be heard coarsely bragging about groping women.

Corsi said Stone had urged him to reach Assange and get him to release whatever he’d been holding back to counter the damaging video.

About a half-hour after The Post published a story about the video, WikiLeaks did, in fact, post the first tranche of thousands of Podesta emails.

If there was evidence that Stone played a role in the timing of the Podesta release, it would support the case that there was a conspiracy.

Stone has denied knowing anything about the tape in advance or playing a role in the timing of the Podesta release.

Corsi also told investigators that he believed he had played a role in getting WikiLeaks to release the Podesta emails — though he offered conflicting accounts about how he might have done so, according to the report.

Looking for corroborating evidence, with Corsi’s help, prosecutors constructed a detailed timeline of Corsi’s emails and phone calls in that period. They sought out Corsi’s contacts, looking for anyone who could be a go-between to WikiLeaks.

On Oct. 3, 2018, an FBI agent accompanied by a local sheriff’s deputy knocked on the back gate of the home of James and Joanne Moriarty in the Piney Woods, a rural region of eastern Texas.

The couple had lived in Libya before the 2011 fall of ruler Moammar Gaddafi and had served as sources for Corsi as he worked on articles about what he felt were the failures of the Obama administration in that country.

In the days leading up to the Oct. 7, 2016, WikiLeaks release, they communicated several times with Corsi about an article he was writing for the right-wing online outlet World Net Daily, James Moriarty told The Post.

Moriarty said he and his wife greeted the FBI agent coldly, first complaining that they did not see the agent as “any kind of good person” because he had come to their home wearing a weapon under his suit jacket.

Moriarty said they then spent three hours telling the agent about their experience in Libya, where he said they were detained by militants, and how they believed they had been relentlessly targeted by the U.S. government since they returned to Texas.

“The invasion of terrorists into the United States is real and present,” Moriarty said. “I told him about this and I told him that, now that he knows, he has to pass it along to other government agencies, including the White House, or he will be guilty of felonious acts.”

Moriarty said he and his wife ultimately consented to be interviewed. The agent spoke to them separately for a total of about 20 minutes. They both told the agent they had not connected Corsi to Assange.

The dead end in the Piney Woods was typical.

According to Mueller’s report, investigators could find “little corroboration” for Corsi’s claim that Stone had urged him to help spur the Podesta email release.

In one interview, Corsi suggested he might have publicly tweeted a message that he thought Assange would read.

“Our Office was unable to find evidence of any such tweets,” Mueller wrote.

Gray said the frustration of the prosecution team became obvious. At one meeting, Rhee, a former partner at the prominent law firm WilmerHale, began to raise her voice as Corsi insisted he clearly remembered a conversation he had with Malloch a few months earlier, but not a key conversation he had shortly afterward with Stone.

“That was six months ago,” she said, according to Gray’s notes.

“We find what you’re saying is lacking,” Zelinsky added.

By their final meeting on Nov. 2, 2018, the prosecutors made their concerns clear. They lectured Corsi for about 20 minutes about the need to stick to definite facts.

Then they started in again: Were you a source about WikiLeaks for Roger Stone?

Corsi, who had grown increasingly uncomfortable as the prosecutors spoke, had trouble answering clearly.

After about five minutes, the prosecutors declared they were done, Gray said.

By the end, Mueller’s team had uncovered a wide array of contacts between Trump’s orbit and Russia — contradicting post-election claims from Trump’s representatives that there had been none.

They did not find a crime to charge.

According to the report, prosecutors concluded that Page had formed relationships with Russian intelligence officials before the campaign and that he may have been targeted in 2016 by Russian officials because of his Trump campaign tie. They had trouble nailing down everything he did in Moscow during a July 2016 visit, they wrote.

But the investigation did not establish he coordinated with the Russian effort in 2016. After the report’s release, Page said he was not surprised, calling his Russia interactions a “big nothing­burger.”

Mueller’s team also analyzed whether Trump Jr.’s meeting with the Russian lawyer broke campaign finance law prohibiting foreign contributions. They determined they would not be able to prove it did. They also said they could find no connections between the meeting and other Russian efforts to interfere in the election.

Investigators struggled to determine the motive of Manafort’s contacts with Kilimnik, interactions that went “very much to the heart” of the special investigation, prosecutor Andrew Weissmann said in a court hearing in February.

[How Manafort’s 2016 meeting with a Russian employee at New York cigar club goes to ‘the heart’ of Mueller’s probe]

They were hampered by not only his lies, according to the report, but his use of encrypted messaging apps. Mueller ultimately did not find sufficient evidence to prove that Manafort or any other Trump associate acted as an agent of the Russian government.

Stone is scheduled to go on trial in November for lying to Congress, obstructing an official proceeding and witness tampering over allegations he attempted to intimidate Credico.

Key details about his case were redacted from the report because of a gag order imposed by the judge, which has also limited what Stone can say in his defense. He is, however, selling T-shirts to fund his legal defense that read, “Roger Stone did nothing wrong!”

It is not clear why Mueller’s team did not file the false-statement charges they threatened against Corsi. Much of the report dealing with their interactions with him has also been redacted by the attorney general, citing possible harm to an ongoing investigation. The report does not specify whether the redactions are related to Stone’s case or other continuing matters.

Corsi said last week that the experience showed the probe was a “fraud from the start.” He said only a “criminal” would urge him to plead guilty to charges that could not be proved in court.

Gray said he believes it would be inappropriate to charge Corsi because he has a faulty memory and noted that prosecutors gave him extensive opportunities to amend their answers.

“They pushed and pushed,” he said. “But at the end of the day, they threw up their hands and said, ‘We can’t use any of this.’ ”

Tom Hamburger contributed to this report.