The U.S. Federal Bureau of Investigation has issued a public call seeking victims of BitConnect, a cryptocurrency-adjacent alleged ponzi scheme that exploded worldwide over the course of 2017. The operation took in an estimated $1.5 billion before its sudden shutdown—an apparent ‘exit scam’—in early 2018. The FBI notice was first released on February 12, and confirms that the law enforcement agency is investigating the scheme after earlier hints to that effect.

BitConnect was just one of a slew of alleged scams that leveraged a mix of hype and ignorance to entice victims during the frenetic bull market of 2017. But its global reach and aggressive marketing made it a symbol of that wider corruption. That status was cemented, of course, by the infamous video of BitConnect “investor”/victim Carlos Matos leading a manic chant and mocking his wife’s skepticism at a BitConnect event.

For all its publicity, BitConnect remains mysterious in one key way—it’s still unclear who actually masterminded the scheme. So far, enforcement and investigative action has focused on a network of regional promoters, who in some cases may not have themselves been aware of the fraudulent nature of the scheme.

Trevon James, a U.S. YouTube personality, had previously stated he was being investigated by both the SEC and FBI. Australian authorities have also moved against John Bigatton, a regional promoter there.

Divyesh Darji, the head of BitConnect’s India operations, was arrested in Dubai last August and is alleged to have been a key operator. Even if that’s true, he was likely one among several. An active investigation by the FBI may be the last, best chance to find his collaborators and turn the page on one of crypto’s darkest chapters.