A letter released Monday by Republican Senators Chuck Grassley and Lindsey Graham offers an important clue.

In the heavily redacted, declassified version of the letter, which outlined why Graham and Grassley asked the Justice Department to consider opening a criminal investigation into Steele’s communications with the FBI, the senators allege that “Clinton associates” were “feeding Mr. Steele accusations” against the Trump campaign, thereby calling into question Steele’s credibility as a neutral source.

Two sources familiar with the matter, who requested anonymity because they were not authorized to speak to the press, told me the redacted portions of the letter refer to the information compiled by Shearer—for the first time revealing some of the key details that were redacted in the original letter. Shearer’s information was passed to Steele by Winer. Winer, a friend of Steele’s, was then serving as the special envoy for Libya, and had previously passed Steele’s Russia and Ukraine reports along to the State Department’s Europe bureau between 2014 and 2016. Shearer, Blumenthal, and Winer did not immediately respond to requests for comment.