Michael Flynn's sentencing memo, filed yesterday with the most intriguing and interesting parts redacted by special counsel Robert Mueller, provided yet another frustrating glimpse into an investigation that seems at times almost maddeningly opaque. It made clear that Flynn was cooperating in three criminal investigations—and that he had cooperated extensively—but shed little light on the "what" or the "how."

Amid the flurry of revelations from special counsel Robert Mueller’s investigation of Russia’s role in the 2016 campaign, it’s worth revisiting the loose ends of his probe. Specifically, focusing on questions that remain mysteries to us but that clearly Mueller himself knows by this point—the Rumsfeldian “known unknowns”—provides particular clarity as to where the investigation will head next.

SIGN UP TODAY Sign up for the Daily newsletter and never miss the best of WIRED.

Decoding Mueller’s 17-month investigation has been a publicly frustrating exercise, as individual puzzle pieces, like Flynn's sentencing memo, often don’t hint at the final assembled picture—nor even tell us if we’re looking at a single interlocking puzzle, in which all the pieces are related, or multiple, separate, unrelated ones.

The sheer breadth of alleged, unrelated criminality by so many different Trumpworld players—from Paul Manafort’s money laundering and European bribes to Michael Flynn’s Turkish conspiracies to Michael Cohen’s tax fraud to even the indictments of the first two members of Congress to endorse Trump, representatives Chris Collins and Duncan Hunter—make it particularly difficult to disentangle what might have transpired at Trump Tower and the White House.

Mueller’s investigation, though, has been remarkably focused and consistent straight through—zeroing in on five distinct investigative avenues: money laundering and Russian-linked business deals; the Russian government’s cyberattack on the DNC, other entities, and state-level voting systems; its related online information influence operations, by the Internet Research Agency; the sketchy contacts by Trump campaign and transition officials with Russia; and the separate question of whether Trump himself, or others, actively tried to obstruct justice by impeding the investigation of the above.

A sixth investigative avenue was opened this spring by federal prosecutors in the Southern District of New York, where Michael Cohen pleaded guilty to violating campaign finance laws by paying hush money to Stormy Daniels and others—which he says occurred at Trump’s instruction.

Mueller’s careful, methodical strategy often only reveals itself in hindsight, as the significance of previous steps becomes clear with subsequent ones. Examining today the totality of what Mueller and prosecutors have shown thus far illuminates numerous areas of clear interest.

Despite the massive revelations—and more than 300 pages of a “Mueller report” that has already been written through court filings—there remain very basic details we still don’t know, starting with three overarching concerns:

1. Is Matt Whitaker overseeing the Russia probe—and is his appointment as attorney general even legal? It’s remarkable how little we know about the status of the acting attorney general, Matt Whitaker, whose appointment is being challenged in multiple legal forums currently as unconstitutional, and whether he’s actively overseeing the Russia investigation. Under immense pressure, Whitaker—who has publicly criticized the Mueller probe and whose appointment seemed designed to hinder Mueller—announced soon after his appointment that he would seek the guidance of Justice Department ethics lawyers, but the department has refused to say whether he’s done so. As Tom Goldstein, one of DC’s most respected Supreme Court attorneys and observers, wrote to the Court, “It is a constitutional crisis even if we are distracted from and dulled to it.”

2. Is Commerce Secretary Wilbur Ross involved in any of this? Scandals come and go so quickly in the Trump administration that it’s hard to keep them straight, but it’s worth revisiting that investigative journalists, primarily at Forbes, have spent the year documenting myriad sketchy financial dealings by Cabinet member and billionaire Wilbur Ross, including his apparent ties to a Cyprus bank controlled by Russian oligarch Viktor Vekselberg, who has been mixed up with Michael Cohen and whose companies funneled Cohen more than $4.4 million for “consulting services” after Trump’s election. (The same Cyprus bank was a key conduit of Paul Manafort’s alleged money laundering, and cooperated with Mueller’s investigation.) As commerce secretary, Ross also maintained part ownership in a shipping company owned by another Russian oligarch who was under sanctions by the US government. While Ross’ scandals have thus far appeared separate from Trump’s, he adds to the unusually large number of Trump associates with complex financial ties to Russia. And Ross’ continued well into his time in the Cabinet, providing another potential point of leverage for Russian influence.