After two years of near-total silence, Robert Mueller spoke, and people who know him want to know why. Last Thursday, BuzzFeed published an extraordinary report alleging that Donald Trump had instructed Michael Cohen to lie to Congress about plans to build a Trump Tower in Moscow, prompting an equally extraordinary denial from the special counsel’s office. The “description of specific statements to the special counsel’s office, and characterization of documents and testimony obtained by this office, regarding Michael Cohen’s congressional testimony are not accurate,” said special-counsel spokesperson Peter Carr. BuzzFeed, meanwhile, is standing by the story. On Tuesday, the outlet dumped a cache of documents related to the Moscow project, including texts and architectural renderings, as if to say: we’ve got the goods.

Days later, veterans of the Justice Department are still trying to make sense of the stare-down. “Mueller wouldn’t have done that unless he felt compelled to do it. He doesn’t really care what the media reports; he doesn’t really care what the rumors are,” said Robert Grant, a former top F.B.I. agent who used to work with Mueller. “For him to go out and do that, that’s extraordinary—which means his team must have convinced him that [they] had to correct that because of its potential impact on the investigation. And I don’t know what those impacts might be.”

There have, after all, been countless Trump-Russia bombshells since Mueller was appointed in May 2017, and the special counsel’s office has remained virtually mum. Why step in now? “The fact that the Mueller team was willing to make a statement indicates that they must have thought that this was a serious error, and maybe even one that was unfair to witnesses and subjects of the investigation,” said Harry Sandick, a former federal prosecutor for the Southern District of New York. Eric Columbus, a former top-ranking attorney in the Justice Department, agreed. “It seems to me that Peter Carr did that with the intention of conveying that the story was largely inaccurate.”

To lay ears, the Mueller retort sounded vague, lawyered, and evasive. Even BuzzFeed seemed confused about the lack of specifics. Shortly after Mueller’s office issued the statement, editor-in-chief Ben Smith called on the special counsel’s office to clarify its concerns. “We really urge the special counsel to make it clear what he’s disputing,” he said Friday evening in an interview with CNN. The special counsel did not respond.

For D.O.J. veterans, however, Mueller’s silence spoke volumes. Ordinarily, explained Grant, Mueller “sees nothing but risk” in speaking to journalists. It is a “high-wire act”—especially when a media report sparks calls for congressional investigations and even impeachment, like the BuzzFeed story did. If Mueller’s team was to identify specific inaccuracies in the BuzzFeed story, it might be seen as tacit confirmation of other details. “I assume he doesn’t want to play that game,” Sandick said. “One of the virtues of the way that the Mueller team has conducted things is to be very careful in not leaking, and not making public statements—that it is a recognition that those kinds of things don’t help bring about justice. They are not fair to people who are in the process. And so, having done all of that, it seems like: why change the approach now?”

Jennifer Rodgers, another former federal S.D.N.Y. prosecutor, offered one potential theory. The two BuzzFeed reporters, Jason Leopold and Anthony Cormier, cited two federal law-enforcement officials as their source for the allegation that Cohen “told the special counsel that after the election, the president personally instructed him to lie” to Congress. They also alleged that the special counsel’s office learned of the instruction “through interviews with multiple witnesses from the Trump Organization and internal company e-mails, text messages, and a cache of other documents.” Perhaps, she suggested, Mueller’s team was alarmed by the implication that the sources were inside their office, or that they have hard evidence of Cohen’s conversations with Trump.