A federal judge on Tuesday told prosecutors they did not have to make public highly classified transcripts of Michael T. Flynn talking about sanctions with the Russian ambassador in December 2016.
The judge’s decision means that the exact words that Mr. Flynn, President Trump’s first national security adviser, and Sergey I. Kislyak, formerly Russia’s top diplomat in the United States, exchanged during the presidential transition will remain secret.
The men spoke shortly after the Obama administration placed sanctions on Russia for interfering in the 2016 presidential election. Mr. Flynn later denied to Trump administration officials and the F.B.I. that they discussed sanctions. The transcripts would have demonstrated the extent of Mr. Flynn’s lies.
The judge, Emmet G. Sullivan of the United States District Court for the District of Columbia, who is overseeing Mr. Flynn’s case, had previously ordered prosecutors to disclose the information by the end of last month.
But prosecutors balked and told the judge in a court filing that the “government further represents that it is not relying on any other recordings, of any person, for purposes of establishing the defendant’s guilt or determining his sentence, nor are there any other recordings that are part of the sentencing record.”
The transcripts came from a secret F.B.I. wiretap of Mr. Kislyak. If prosecutors had disclosed them, they would have revealed what Russian diplomats living in the United States certainly already knew or suspected: The F.B.I. listens to their calls. Such wiretaps are approved by the secretive Foreign Intelligence Surveillance Court, and they are among the government’s most closely held secrets.
Mr. Trump fired Mr. Flynn after he lied to the vice president and other administration officials about the substance of the calls. In December 2017, Mr. Flynn pleaded guilty to lying to the F.B.I. after agents interviewed him about what was said on those calls. Mr. Flynn awaits sentencing.
Why he decided to lie to the White House remains unclear. Federal prosecutors said in a court filing late last year that Mr. Flynn lied to the agents because “by the time of the F.B.I. interview, the defendant was committed to his false story.”
At the time, the calls set off alarms among senior Obama administration officials that Mr. Flynn and the incoming Trump administration were interfering in policy before taking office.