What is known, based on press leaks and a letter Senate Judiciary Committee Chairman Chuck Grassley sent Lynch, is that in March 2016, the FBI received a batch of hacked documents from U.S. intelligence agencies that had access to stolen emails stored on Russian networks. One of the intercepted documents revealed an alleged email from then-DNC Chairwoman Wasserman Schultz to an operative working for billionaire Democratic fundraiser George Soros. It claimed Lynch had assured the Clinton campaign that investigators and prosecutors would go easy on the presumptive Democratic presidential nominee regarding her use of a private email server while serving as secretary of state. Lynch allegedly made the promise directly to Clinton political director Amanda Renteria.
The FBI apparently took the document seriously but never interviewed anyone named in it until Clinton’s case was closed by Comey in July 2016. The next month, the FBI quizzed Lynch informally about the allegations. Comey reportedly also confronted the attorney general with the sensitive document and was told to leave her office after getting a frosty reception. No other parties mentioned in the document have been interviewed by the FBI.The current theory is that it was this intercepted transmission, rather than the tarmac meeting, that led Comey to go off the reservation and cut Lynch out of the loop in his decision to go public with investigations of Clinton. He claims to have begun worrying about Lynch in September 2015, when she asked him not to refer publicly to an "investigation" of Clinton but instead to call it a "matter." Comey presumably didn't know any more than we now know whether the intercepted message was real or a fabricated Russian ruse, but he obviously found it credible enough to support his pre-existing doubts about Lynch.
I don't know quite what to think of Comey. The man blew his ethical obligations six ways from Sunday, but he does not seem to have been operating as a straightforward Clinton or even Democratic operative. I wonder if even he knows exactly what he was up to. My guess is Lynch did, though.