Mimi Rocah, a former federal prosecutor in the Southern District of New York, said that any information Mueller needed from Flynn has probably “already been locked in” before the grand jury, and the former general is most likely no longer of investigative value to Mueller. “I’m sure it’s no accident that Manafort just pled,” Rocah said, referring to the president’s former campaign chairman Paul Manafort, who pleaded guilty on Friday to conspiracy and obstruction charges and is now cooperating with Mueller. “Flynn likely had information on Manafort and now that Manafort has pled, Flynn isn’t needed as much.”

Flynn served as a high-level surrogate and adviser to Trump during the election, and was a member of Trump’s transition team before he was appointed national-security adviser last January. He was in the job for a little more than three weeks before reports surfaced that he had discussed the issue of sanctions with Kislyak during the transition period, despite repeated denials—including to Vice President Mike Pence—that the topic had ever come up. Intelligence officials, however, had listened in on the Flynn-Kislyak calls as part of their routine eavesdropping on foreign diplomats, and knew that Flynn had lied—he had, in fact, asked Kislyak “to refrain from escalating the situation in response to sanctions that the United States had imposed against Russia” in December 2016, according to an indictment filed by Mueller’s office last year to which Flynn pleaded guilty. In response, Kislyak told Flynn that Russia had “chosen to moderate its response to those sanctions as a result of his request,” the indictment said.

The veteran journalist Bob Woodward touched on the Flynn-Kislyak calls in his new book, Fear. Not only were the sanctions discussed in every phone call, Woodward reported, but transcripts obtained by the White House in February 2017—as they were weighing whether to fire Flynn—showed that it was Flynn, and not Kislyak, who first brought up the sanctions that President Barack Obama had issued in December in response to Russia’s election interference. Then–Acting Attorney General Sally Yates warned White House Counsel Don McGahn that Flynn had misled the FBI about the calls. Still, the White House waited 17 days to fire Flynn, and the day after he was ousted, Trump met with then–FBI Director James Comey and asked if he would consider letting Flynn “go.” That 17-day gap (and Trump’s subsequent request to Comey) has come under scrutiny by Mueller.

Once he began cooperating with prosecutors, Flynn seemed like he was in a position to answer some of the biggest lingering questions in the Russia probe: Did Trump direct Flynn to dangle the easing of sanctions in front of Kislyak during the transition period? And did the president know that Flynn had misled the FBI when he denied ever discussing sanctions with Kislyak? (If Trump knew the extent to which Flynn was in the FBI’s crosshairs when he asked Comey, whom he later fired, to consider “letting Flynn go,” that could dramatically bolster the obstruction case federal prosecutors are building against him.) Furthermore, why did the White House wait nearly three weeks to fire a high-level adviser who was, according to Yates, vulnerable to being blackmailed by the Russians? Flynn also may have had knowledge about a “peace plan” that involved lifting sanctions on Russia in return for Moscow withdrawing its support for pro-Russia separatists in eastern Ukraine, which was allegedly hand-delivered to him by the president’s longtime lawyer, Michael Cohen.