Today’s guilty plea by Rick Gates might be one of the least surprising developments in the Mueller investigation: It had been clear that the former Trump campaign aide would likely seek a deal almost since the day Gates and his business partner and former Trump campaign chairman Paul Manafort were indicted in October, and we’ve seen reports for weeks that negotiations between Mueller and Gates have been underway.

The move does, though, apply new pressure to Manafort, who will now face in court not just the bank records that originally led to his indictment but also testimony from his former close associate and accomplice in the money-laundering scheme that allegedly involved upward of $60 million. When it comes to Manafort, Gates—who was also a Trump campaign and transition official—knows where the bodies are buried.

That only became more obvious on Thursday, when the special counsel unveiled a new set of charges against Manafort and Gates, a so-called superseding indictment that added more specifics to the money-laundering and bank fraud case brought against them in October. Coupled with the Gates plea, it’s clear that Manafort’s legal problems are likely to get much worse.

Indeed, Mueller's probe is accelerating. Yesterday's new indictment—together with Tuesday’s guilty plea by Alex van der Zwaan, a Dutch lawyer associated with Gates, Manafort, and Ukraine; last Friday's bombshell indictment of 13 Russians and three Russian entities; and now the Gates plea—underscores that Mueller is applying the full strength of the US government’s resources to follow every thread of the investigation. His indictments have astounded Washington with their level of specificity and detail, delivering a litany of facts that he’s confident he can prove in court beyond a reasonable doubt. His hammering of the Dutch lawyer for lying to investigators continues his consistent message that the special counsel’s office will treat seriously anyone who stands in their way.

But almost as intriguing are the threads that Mueller has left hanging, the questions that go unanswered in otherwise highly specific court documents—like the identity of “Person A” in the charges filed against van der Zwaan Tuesday, a veiled reference to someone else involved in the Gates/Manafort/Ukraine milieu who might now face legal jeopardy in the investigation.

Mueller clearly knows where this investigation is going and is methodically building it brick by brick: His first wave of charges, against Manafort, Gates, and George Papadopoulos, established that the Trump campaign had been lying about its contacts with Russians; his second wave—the guilty plea by Michael Flynn—established that those lies extended to figures inside the White House; his third wave of charges, against the Internet Research Agency, establishes that there was a criminal conspiracy to help Trump and undermine Hillary Clinton. Any Americans who knowingly participating in that conspiracy will also, presumably, be vulnerable to prosecution.

None of the rest of us knows where this investigation is heading, not even the targets of the investigation. Three times now Mueller—in the most watched investigation in history—has charged and gotten guilty pleas from people who weren’t even on our radar: Papadopoulos and Richard Pinedo, a Californian who pleaded guilty last Friday to unwittingly aiding the Russians with identity theft, as well as the Dutch lawyer who pleaded guilty earlier this week.

Last summer, I outlined 15 “known unknowns” in the Trump/Russia investigation, unanswered but knowable threads that Mueller’s team could be expected to pull on. The answers to many of those questions are still not public. Yes, we’ve received significant new information about how Dutch intelligence tipped off the US to Russia’s hacking efforts. But we’ve still not seen charges concerning active cyber intrusions—most notably, the hacking of the Democratic National Committee’s computers and the stealing of Clinton campaign manager John Podesta’s emails—one of at least five related probes Mueller is leading right now.