There was a potential bombshell buried in the first round of indictments issued on Monday by special counsel Robert Mueller as part of his investigation into possible collusion between the Trump campaign and Russia.

But it was not in the highly anticipated indictment against Trump’s former campaign manager, Paul Manafort, for allegedly laundering payments from a pro-Russian Ukrainian political party. Instead, the most potentially explosive nuggets from the day’s news belonged to a plea deal that no one saw coming.

Former foreign policy adviser George Papadopoulos pleaded guilty to lying to investigators about his contacts with apparent intermediaries for Russia after being arrested in July—a development that had not been previously reported, despite the intense interest in Mueller’s probe. Papadopoulos is described in court documents as a “proactive cooperator,” which could be an indication that he went so far as to wear a wire in the months since he was charged.

The 14-page statement of the offense released by prosecutors contains three key portions of Papadopoulos’ admissions: a description of receiving an offer for “dirt” on Hillary Clinton available in “thousands of emails;” a potentially critical May 2016 email forwarded to Trump staffers that promised “cooperation” from the Russians; and a yet-to-be-described follow-up phone call between Papadopoulos and someone listed merely as his campaign supervisor. If there is a smoking gun lurking somewhere in Monday’s news, it is likely to emerge from these exchanges.

Here is the description of the possibly critical meeting between Papadopoulos—then a foreign policy adviser who had been described by Trump as an “excellent guy”—and an unnamed “overseas professor who …. Papadopoulos understood to have substantial connections to Russian government officials.” (The Washington Post reported on Monday that the professor was likely Joseph Mifsud, the director of the London Academy of Diplomacy.)

As the Post noted, this exchange occurred one month after a group affiliated with Russian intelligence appears to have hacked into the emails of Hillary Clinton campaign chairman John Podesta. Those emails would later be leaked as part of an overall Russian attempt to interfere with the election, according to U.S. intelligence officials.

At this point in the campaign, Mueller’s team noted, Papadopoulos continued to have communication with Trump’s campaign staff in an attempt to set up a meeting between Trump and Putin. (In emails that were not sent to Papadopoulos, Trump’s staff blew off his request.) But Papadopoulos then shifted to trying to set up a meeting between a member of the campaign and a Russian emissary. Mysteriously, the statement of offenses at this point stopped describing what further attempts, if any, there were by Papadopoulos and the campaign to secure “dirt” on Clinton.

It did, though, mention additional exchanges—which occurred a little more than one week after the offer for “dirt” on Clinton—between the professor and Papadopoulos that were then passed along to Trump campaign staff. In one email, a “Russian Ministry of Foreign Affairs Connection” told Papadopoulos that the ministry was “open for cooperation.” That email was then forwarded to a person listed only as “High-Ranking Campaign Official,” as well as someone listed as a “Campaign Supervisor.”

The day after receiving the “May 4 MFA Email” about potential “cooperation,” Papadopoulos had a call with the “Campaign Supervisor.” Notably, the details of that phone call are omitted from the statement, along with any further details of possible conversations about the “dirt” that was on offer.

What might all this mean? It could mean nothing. But given what we already know about Donald Trump Jr.’s eagerness for potentially incriminating information from the Russians, it seems just as likely that there was further discussion of the potential “cooperation” as well as the “dirt” and the “thousands of emails.”

“It would be very odd of Papadopoulos [not to bring it up with campaign officials] given how hard he was trying to cultivate the people on the campaign,” Georgetown Law professor and former federal prosecutor Julie O’Sullivan told me.

O’Sullivan interpreted that conversation about cooperation as being about the meeting itself and not the possible “dirt.” But she noted that both possible readings were plausible. “It does seem odd to me that that would be the end of it,” she said. “It’s odd that he gets that [offer] and there’s nothing in this [statement] about him following up at all.”

If that May 5 phone call between Papadopoulos and the “Campaign Supervisor”—or some other yet to be disclosed conversation—included a discussion of “dirt” and potential “cooperation”—e.g., collusion—why wouldn’t Mueller’s team have put it in the statement?

First of all, there is no obligation to include it, since Papadopoulos had already confessed to the crime. But there may also be strategic reasons not to include such information, as Mueller tries to build a concrete case, while navigating around a mercurial president who has expressed open hostility for his work.

“You don’t necessarily want to put everything out there,” O’Sullivan said. “This is a very early stage.”

She added: “Once you get into, ‘he got this information and he started talking to senior campaign aides about getting potential campaign dirt on Hillary,’ that changes the whole complexion of this information.”

O’Sullivan said it could also be “a shot across the bow” of other campaign staff.

Samuel W. Buell, a Duke University law professor and former Enron prosecutor, said federal prosecutors can sometimes hold back testimony because “maybe you don’t want to lock in [the story] too tight for fear if it even changes slightly you’re creating cross examination material.” Interviews with cooperating witnesses are not normally recorded in federal cases, Buell said, so there is no verbatim record for defense attorneys to point to if inconsistencies between trial testimony and an original account emerge. There are FBI reports—known as 302s—but not transcripts of interviews. Putting unnecessary information about a person’s testimony regarding phone calls or meetings could serve to potentially impeach his testimony later on if details change at all. Emails, though, never change.

“You’re not holding it back because you think it’s intimidating to hold it back, you’re holding it back because you’re just being really careful about this guy’s testimony,” Buell told me.

The fact that prosecutors included the call, though, seems potentially significant, particularly as the White House dissembles about the ties between Papadopoulos and the campaign.

At a press briefing on Monday, White House press secretary Sarah Huckabee Sanders discounted the contacts between Papadopoulos and the “Campaign Supervisor,” the emails between him and campaign officials about the promise of cooperation, and emails from various campaign officials encouraging setting up a meeting with the Russians. Huckabee Sanders said Papadopoulos had “nothing to do with the activities of the campaign,” and that he was merely a member of an advisory board, a volunteer official, and nothing more. “Again, there are no activities or official capacity in which the Trump campaign was engaged in any of these activities,” she said. The email and phone record listed in the statement of facts shows that is demonstrably false—Trump campaign officials were clearly involved with Papadopoulos on these issues.

If the White House is lying about this element of the Papadopoulos statement, what else might they be lying about?

Read more about the investigation into the 2016 campaign.