Politico reports today that according to a knowledgeable source, Facebook knows that “shadowy Russian buyers” purchased advertisements on its platform that aimed to influence the 2016 presidential race. The ads, we learn, praised Donald Trump, Green Party candidate Jill Stein, and Hillary Clinton’s Democratic primary rival Bernie Sanders — even after he dropped out of the race. Although many of the ads said nothing about Clinton, they all either boosted a Clinton rival, or were otherwise aimed at sowing divisions on issues prevalent in the campaign.

The Politico scoop is just the latest tidbit of information we have learned about Facebook’s role in disseminating Russian-backed propaganda aimed at disrupting the 2016 presidential campaign, following its belated disclosure earlier this month that Russian entities had indeed used fake accounts to buy political ads.

Which raises the question: How much can Facebook tell us about what really happened when it comes to Russian sabotage of the 2016 election?

Mark Warner, the Democratic co-chair of the Senate Intelligence Committee, which is investigating Russian election interference, has been arguing lately that Facebook needs to come clean. It needs to publicly disclose the full scope and scale of how Russian entities used its social networking platform to spread fake news and propaganda in order to sow divisions among American voters and influence the outcome of the presidential election.

Politico’s scoop confirms that Warner is right.

Our intelligence services have concluded with high confidence that Russia tried to sabotage our election. And Americans are owed a full accounting of how those efforts were carried out. Russian exploitation of Facebook is just one piece of the story. But it’s a crucial one, given the social media platform’s ubiquity, and how it is used by ordinary people to share news, and by political campaigns to cultivate supporters.

There’s a great deal the public still needs to learn about this. Facebook can tell us a lot more — and it should, either at congressional hearings, or via more forthcoming and detailed public statements, or both.

What we do know has been revealed only in slow drips and episodic, anonymous revelations like the one to Politico. And Facebook itself has been slow and sparing with transparency. It was only three weeks ago — 10 months after the election — that the company first revealed that, contrary to its earlier denials, it had uncovered approximately $100,000 in spending on roughly 3,000 ads between June of 2015 and May of 2017, by hundreds of affiliated fake accounts “likely operated out of Russia.”

Given the billions that were spent in the U.S. on the presidential campaign, $100,000 might not sound like a lot. But according to a tally by the Daily Beast, those 3,000 ads “were likely seen by a minimum of 23 million people and might have reached as many as 70 million,” meaning that “up to 28 percent of American adults were swept in by the campaign.”

Here are some of the things we still don’t know.

We don’t know who paid for the ads on Facebook and, crucially, how and why the purchasers targeted certain Facebook users to see them in their feeds, and whether they worked with anyone in the United States to develop those lists of targets. This means that, because Facebook continues to insist on opacity, all of those millions of Facebook users still don’t know who was actually targeting them, and why they were chosen to be targeted.

Those unknowns lie at the heart of the investigation — and both Special Counsel Robert S. Mueller III and Congressional investigators know it. Following a search warrant, Facebook turned over data to Mueller’s team that “included copies of the ads and details about the accounts that bought them and the targeting criteria they used.”

That’s obviously critical to Mueller’s investigation. But it is also information that the American public deserves. As Nate Persily, a Stanford professor and election law expert, argues: “It doesn’t seem to be a terribly chilling idea to say that we should be able to know how much money is being spent on election-related advertisements online, and we ought to be able to see what those advertisements were and who they were targeted to.”

Meanwhile, Warner knows that what Facebook has publicly revealed is only a fraction of what the public has a need to know right now. Warner has called Facebook’s belated disclosures just the “tip of the iceberg.”

And so, Warner has also called for the Facebook ads themselves to be made public. He has argued that the public not only has a right to know who purchased the ads, but also why some Facebook users were selected to see the ads known as “dark posts,” which other, non-targeted users don’t see. “If you’re for or against a candidate, or for or against a cause, you ought to be able to see the content that’s being launched against you, particularly if it comes from a foreign source,” he told CNN on Sunday.

Facebook may well be the singular source for this information. As Wired reported this summer, investigators could learn “as much from platforms like Facebook as from the Trump campaign” about unknowns such as who bought the ads, and the entities to whom Facebook extended a line of credit to accept payment for ads.

But Facebook retains far more than just that information. As Wired also reported: “Facebook also allows political advertisers to upload their own voter lists for targeting purposes. Investigators could ask the company whether any advertisers used duplicate lists to disseminate pro-Trump or anti-Clinton ads.” In other words, Facebook may be able to tell investigators whether Russian-financed advertisers were using the same target lists as, say, the Trump campaign did in its own advertising.

Warner has called for public hearings for Facebook executives, and is working on legislation that would subject ads on Facebook to the same campaign finance disclosure requirements imposed on television and radio ads. In the meantime, though, 68 percent of American adults use Facebook, and many of them were likely, in one way or another, exposed to the Russian efforts. The company at least owes the public an accounting of how foreign actors exploited its platform to sabotage our election.