WASHINGTON — Michael Sussmann, a prominent cybersecurity lawyer with ties to Hillary Clinton’s presidential campaign, was acquitted on Tuesday of lying to the F.B.I. in 2016 when he shared a tip about possible connections between Donald J. Trump and Russia.
The verdict was a significant blow to the special counsel, John H. Durham, who was appointed by the Trump administration three years ago to scour the Trump-Russia investigation for any wrongdoing.
But Mr. Durham has yet to fulfill expectations from Mr. Trump and his supporters that he would uncover and prosecute a “deep state” conspiracy against the former president. Instead, he has developed only two cases that led to charges: the one against Mr. Sussmann and another against a researcher for the so-called Steele dossier, whose trial is set for later this year.
Both consist of simple charges of making false statements, rather than a more sweeping charge like conspiracy to defraud the government. And both involve thin or dubious allegations about Mr. Trump’s purported ties to Russia that were put forward not by government officials, but by outside investigators.
The case against Mr. Sussmann centered on odd internet data that cybersecurity researchers discovered in 2016 after it became public that Russia had hacked Democrats and Mr. Trump had encouraged the country to target Mrs. Clinton’s emails.
The researchers said the data might reflect a covert communications channel using servers for the Trump Organization and Alfa Bank, which has ties to the Kremlin. The F.B.I. briefly looked at the suspicions and dismissed them.
On Sept. 19, 2016, Mr. Sussmann brought those suspicions to a senior F.B.I. official. In charging Mr. Sussmann with a felony, prosecutors contended that he falsely told the official that he was not there on behalf of any client, concealing that he was working for both Mrs. Clinton’s campaign and a technology executive who had given him the tip.
Mr. Durham and prosecutors used court filings and trial testimony to describe how Mr. Sussmann, while working for a Democratic-linked law firm and logging his time to the Clinton campaign, had been trying to get reporters to write about the Alfa Bank suspicions.
But trying to persuade reporters to write about such suspicions is not a crime. Mr. Sussmann’s guilt or innocence turned on a narrow issue: whether he made a false statement to the senior F.B.I. official at the 2016 meeting by saying he was sharing those suspicions on his own.
Mr. Durham used the Sussmann case to put forward a larger conspiracy: that there was a joint enterprise to essentially frame Mr. Trump for collusion with Russia by getting the F.B.I. to investigate the suspicions so reporters would write about it. The scheme, Mr. Durham implied, involved the Clinton campaign; its opposition research firm, Fusion GPS; Mr. Sussmann; and the cybersecurity expert who had brought the odd data and analysis to him.
That insinuation thrilled Mr. Trump’s supporters, who have embraced his claim that the Russia investigation was a “hoax” and have sought to conflate the official inquiry with sometimes dubious accusations. In reality, the Alfa Bank matter was a sideshow: The F.B.I. had already opened its inquiry on other grounds before Mr. Sussmann passed on the tip; the final report by the special counsel, Robert S. Mueller III, made no mention of the Alfa Bank suspicions.
But the case Mr. Durham and his team used to float their broad insinuations was thin: one count of making a false statement in a meeting with no other witnesses. In a rebuke to Mr. Durham; the lead lawyer on the trial team, Andrew DeFilippis; and his colleagues, the 12 jurors voted unanimously to find Mr. Sussmann not guilty.
Some supporters of Mr. Trump had been bracing for that outcome. They pointed to the District of Columbia’s reputation as a heavily Democratic area and suggested that a jury might be politically biased against a Trump-era prosecutor trying to convict a defendant who was working for the Clinton campaign.
The judge had told the jurors that they were not to account for their political views when deciding the facts. The jury forewoman, who did not give her name, told reporters afterward that “politics were not a factor” and that she thought bringing the case had been unwise.
Mr. Durham expressed disappointment in the verdict but said he respected the decision by the jury, which deliberated for about six hours.
“I also want to recognize and thank the investigators and the prosecution team for their dedicated efforts in seeking truth and justice in this case,” he said in a statement.
Outside the courthouse, Mr. Sussmann read a brief statement to reporters, thanking the jury, his defense team and those who supported him during what had been a difficult year.
“I told the truth to the F.B.I., and the jury clearly recognized that with their unanimous verdict today,” he said, adding, “Despite being falsely accused, I am relieved that justice ultimately prevailed in this case.”
During the trial, the defense had argued that Mr. Sussmann brought the matter to the F.B.I. only when he thought The New York Times was on the verge of writing an article about the matter, so that the bureau would not be caught flat-footed.
Officials for the Clinton campaign testified that they had not told or authorized Mr. Sussmann to go to the F.B.I. Doing so was against their interests because they did not trust the bureau, and it could slow down the publication of any article, they said.
James Baker, as the F.B.I.’s general counsel in 2016, met with Mr. Sussmann that September. Mr. Baker testified that he had asked Eric Lichtblau, then a reporter at The Times working on the Alfa Bank matter, to slow down so the bureau could have time to investigate it.
Mr. Sussmann’s defense team offered the jurors many potential paths to acquittal, contending that the prosecution had yet to prove multiple necessary elements beyond a reasonable doubt.
His lawyers attacked as doubtful whether Mr. Sussmann actually uttered the words that he had no client at his meeting with the F.B.I. in September.
That issue was complicated after a text message came to light in which Mr. Sussmann, arranging for the meeting a day earlier, indicated that he was reaching out on his own. But it was what, if anything, he said at the meeting itself that was at issue.
Mr. Baker testified that he was “100 percent” certain that Mr. Sussmann repeated those words to his face. But defense lawyers pointed out that he had recalled the meeting differently on many other occasions.
The defense team also argued that Mr. Sussmann was in fact not there on behalf of any client, even though he had clients with an interest in the topic. And they questioned whether it mattered, since the F.B.I. knew he represented the Democratic National Committee and the Clinton campaign on other issues, and agents would have investigated the allegations regardless.
Midmorning, the jury asked to see a trial exhibit meant to bolster the defense’s argument that Mr. Sussmann did not consider himself to be representing the Clinton campaign. It was a record of taxi rides Mr. Sussmann expensed for the Sept. 19 meeting at F.B.I. headquarters.
He logged those rides to the firm rather than to the Clinton campaign or to the technology executive, Rodney Joffe, who had worked with the data scientists who developed the suspicions and brought them to Mr. Sussmann. Prosecutors asserted that Mr. Joffe was his other hidden client in the meeting.
During the trial, prosecutors had made much of how Mr. Sussmann logged extensive hours on the Alfa Bank matter to the Clinton campaign in law firm billing records — including phone calls and meetings with reporters and with his partner at the time, Marc Elias, the general counsel of the Clinton campaign.
Defense lawyers acknowledged that the Clinton campaign had been Mr. Sussmann’s client for the purpose of trying to persuade reporters to write about the matter, but argued that he was not working for anyone when he brought the same materials to the F.B.I.
In a statement, Sean Berkowitz and Michael Bosworth, two of Mr. Sussmann’s defense lawyers, criticized Mr. Durham for bringing the indictment.
“Michael Sussmann should never have been charged in the first place,” they said. “This is a case of extraordinary prosecutorial overreach. And we believe that today’s verdict sends an unmistakable message to anyone who cares to listen: Politics is no substitute for evidence, and politics has no place in our system of justice.”