According to a Yahoo News investigation, the infamous Seth Rich conspiracy theory was planted in the U.S. by Russian intelligence agents. And after the debunked story made its way to Fox News, network executives were never able to identify the source of their now-retracted story.

The U.S. prosecutor who was in charge of the Rich investigation told Yahoo News that Russia’s foreign intelligence service (SVR) first pushed the false claim that Democratic National Committee staffer Seth Rich was murdered by Hillary Clinton’s goons in retribution for leaking DNC documents to WikiLeaks in a fake intel bulletin sent out in July 2016.

The bunk story, Yahoo reported, was eventually pushed by then-chief White House adviser Steve Bannon, who, less than a year later, texted a 60 Minutes producer that it was a “Huge story… [Rich] was a Bernie guy… it was a contract kill, obviously.”

And two months later, the lie made its way to Fox News—both in on-air segments on Sean Hannity’s show and in a now-retracted digital article by Malia Zimmerman. According to Yahoo’s sources, Fox News executives investigated how that story came to be, but were never able to identify the anonymous “federal investigator” at the center of the entire claim. Per Yahoo News: “The Fox editors came to have doubts that the person was in fact who he claimed to be or whether the person actually existed, said the source.”

Zimmerman is still employed at Fox News and the network has yet to disclose the findings of its internal investigation.