Michael Cohen’s congressional testimony on Wednesday was met largely with skepticism that he had much new to offer on the possible crimes of his former boss, Donald Trump. One potentially significant legal development from Cohen’s congressional testimony has gone overlooked, though. It relates to an obscure legal principal, typically reserved for drug cartels and price-fixing cases, that could hold the key to proving allegations of Russian collusion.

It is a concept known as a “hub-and-spoke” conspiracy, and if Cohen’s testimony is to be believed, it could provide a path for prosecutors to implicate Trump in a foreign conspiracy to influence the 2016 election.

Its relevance to the Russia investigation became clearer on Wednesday, when Cohen provided the strongest public evidence to date linking Trump to foreign election meddling. Cohen testified that during a phone call on July 18 or 19, 2016, Roger Stone told Trump that Julian Assange had given him advanced warning that WikiLeaks would be releasing a trove of hacked Democratic National Committee emails in the next few days. According to Cohen, Trump responded to the effect of “wouldn’t that be great.” WikiLeaks began releasing the emails soon after on July 22. Cohen further testified that Stone frequently reached out to Trump by phone and that Trump was “happy to take his calls.”

On its face, nothing in this testimony implicates Trump in an illegal conspiracy. Cohen did not allege that Trump spoke with WikiLeaks himself, and even if he did, learning ahead of time about the release of stolen emails is unlikely to form the basis of an illegal conspiracy. For this reason, most of the analysis of Cohen’s testimony has focused on other areas of legal exposure, like campaign finance violations and obstruction of justice, while reserving judgment on the more complicated question of conspiracy.

That caution is warranted. Proving a conspiracy is difficult. It requires showing that Trump and others reached an agreement to pursue an illegal objective, something that a single conversation between Trump and Stone about WikiLeak’s publication schedule is unlikely to establish.

Yet if Cohen’s testimony was truthful, it adds one critical piece of evidence to what is publicly known about a potential conspiracy: It establishes a direct line of communication between Trump and Stone regarding hacked Democratic emails. When considered alongside what has already been reported about Stone’s similar communications with WikiLeaks and Russian hackers, it begins to outline a broader web of collusion—one with Stone at the center, Trump at one end, and WikiLeaks and Russian hackers on the others.

When courts are presented with such allegations, they tend to describe them not as a web but as a wheel, with a “hub” at the center and multiple “spokes” extending outward toward a rim. This is where the term hub-and-spoke conspiracy gets its name. It is a conceptual framework developed by courts to help judges and attorneys evaluate complex conspiracies where individual conspirators often have no mutual contacts other than through a central intermediary.

Herein lies the benefit of a hub-and-spoke conspiracy to prosecutors like Robert Mueller. Unlike in a traditional conspiracy, where prosecutors must show that each co-conspirator reached an agreement with the others, a hub-and-spoke conspiracy allows prosecutors to hold various co-conspirators liable for a single conspiracy, even when individual conspirators may have never communicated with one another or known about all aspects of the plan.

While not yet proven, one plausible hub-and-spoke structure appears to be taking shape.

Under this framework, courts hold that “[t]here is no requirement that each conspirator participated in every transaction, knew the other conspirators, or knew the details of each venture making up the conspiracy.” All that is required, according to precedent, is that a given co-conspirator be aware of the existence of some of the other participants and do something in furtherance of the broader, illegal goal. Stated differently, case law says that a hub-and-spoke conspiracy may be established when a central actor (or group) helps direct illegal activities “while various combinations of other people exert individual efforts towards the common goal.”

When coupled with the new revelations about Trump’s conversations with Stone, this hub-and-spoke framework provides the clearest road map yet for how Trump personally could be implicated in a foreign conspiracy to influence the election—even if Trump only communicated about the hacked emails with Stone, and even if the impetus for the hacking originated elsewhere.

While not yet proven, one plausible hub-and-spoke structure appears to be taking shape.

At the center, or “hub,” was Stone, who allegedly communicated about stolen Democratic emails with at least three so-called spokes: (1) Trump, (2) WikiLeaks, and (3) Russian hackers posing as Guccifer 2.0. As to WikiLeaks, the special counsel office has alleged that Stone maintained a back channel to Julian Assange through which he repeatedly discussed the release of stolen Democratic emails. The special counsel has also alleged that Stone communicated with Russian hackers, including by sending a message to Guccifer 2.0 on Sept. 9, 2016, stating that he thought stolen Democratic Congressional Campaign Committee turnout data was “pretty standard.” As Marcy Wheeler has pointed out, Stone’s claims that he only communicated with Russian hackers after they stopped hacking Democratic information is doubtful. According to the DNC’s civil lawsuit, Russian hackers continued breaching the DNC’s servers up through Sept. 22, 2016, two weeks after Stone messaged with Guccifer 2.0

For these connections to implicate Trump, prosecutors will need to establish two things. First, prosecutors will need to show that Trump reached some form of agreement with Stone relating to the hacked emails. Cohen’s congressional testimony helps lay the groundwork for such an agreement insofar as it shows that Trump and Stone communicated frequently and Trump approved of Stone’s WikiLeaks contacts. But prosecutors will likely need more evidence regarding the nature of their communications for any charges to stick.

The second task for prosecutors is to show that any agreement Trump and Stone may have reached related to something illegal and not just something unethical or unpatriotic. An agreement to merely solicit updates from WikiLeaks is likely not illegal. A borderline scenario would be if Trump and Stone agreed to actively coordinate with WikiLeaks about when and how hacked information should be released. That may or may not be illegal—the relevant analysis is complex. A third scenario, which would almost certainly be illegal, is if Trump and Stone agreed to coordinate in some way with Russian hackers. If Trump had any involvement in Stone’s alleged communications with Guccifer 2.0, that would likely implicate him in a broader foreign conspiracy, even if he carefully avoided communicating with anyone other than Stone.

The special counsel’s office has closely guarded what it knows about Stone and Trump’s potential connections to WikiLeaks and Russian hacking. Cohen’s testimony offered little more than one man’s glimpse into one of the deepest and most secretive investigations in U.S. history.

Yet it would be a mistake to minimize the legal significance of what Cohen revealed on Wednesday. Cohen advanced the public’s understanding of the collusion investigation in one critical way: He illustrated that the thread connecting Stone to WikiLeaks and WikiLeaks to Russian hackers made its way into the highest offices of Trump Tower.

As Mueller likely recognized long ago, this could be the first step in implicating Trump in a hub-and-spoke conspiracy.