Still, the content of the 2016 meeting was only revealed by accident due to a redaction error by Manafort’s lawyers, and the significance of the episode to Mueller’s main probe, while hinted at by Weissmann, has yet to be fully explained.

“It’s hard to imagine that something so explosive and central to the mission of his investigation wouldn’t be addressed either in charges against someone (Manafort or others) or in a report,” Mimi Rocah, a former federal prosecutor in the Southern District of New York, wrote in an email. “And the fact that the special counsel hasn’t brought it out but it was only revealed inadvertently, reinforces the idea that [Mueller] is saving it for something else.”

That “something else” could be anything from a line in Mueller’s report to an entire conspiracy charge. “My money is on Mueller including the Manafort efforts as part of the ‘case’ alleging Trump campaign collaboration with the Russians,” Patrick Cotter, a former federal prosecutor who specialized in organized crime, told me in an email. “The question then is, what is the best way to make that case? For myself, I believe a RICO [Racketeer Influenced and Corrupt Organizations Act] indictment would be the appropriate vehicle to bring such a case: charge the campaign as the ‘racketeering enterprise’ and name Trump, Manafort and the rest of the gang as members of the enterprise … straight out of the mob prosecution playbook.”

Read: Collusion happened

Cotter, who is familiar with Mueller’s by-the-book style but has no direct knowledge of his internal plans, said Mueller is more likely to take the “safer route”—laying out all the facts that would support such a case in a report, “but not actually charging the legally plausible but politically nuclear formal criminal case.” Any RICO indictment against the campaign for a conspiracy with Russia “would be the new definition of bold and cutting edge.” The former federal prosecutor Jeffrey Cramer agreed that Mueller could bring a conspiracy case and name Manafort and others as unindicted co-conspirators—but if the evidence doesn’t rise to the level of proof beyond a reasonable doubt, it will likely just be outlined in the report.

A spokesman for the special counsel’s office declined to comment. A lawyer for Manafort didn’t return a request for comment.

Whatever path Mueller decides to take, there is no shortage of lingering questions about Manafort’s role in a potential conspiracy. “This hasn’t been resolved at all,” Representative Adam Schiff, the Democratic chairman of the House Intelligence Committee, told me on Thursday. “What Manafort chose to do was to conceal evidence of collusion from the special counsel’s office and from the court, and then have his lawyer go out on the courthouse steps and say there was no collusion.”

Schiff suggested, moreover, that Mueller knows a lot more about Manafort than his office has so far let on. “We have not had access to Manafort and I don’t know whether we ever will,” he said. “But the special counsel’s office does have information about this.” Schiff added that the lingering questions about Manafort’s role underscore how important it is that Mueller’s final report be provided to Congress—and that the report include all of the underlying evidence Mueller collected, regardless of whether it results in a conspiracy charge. “Our standard is not whether there is proof beyond a reasonable doubt,” Schiff said, “but whether there is a risk to national security.”