In the season 4 opener "Herrenvolk", X's position as an informant is discovered by the Syndicate. When suspicion arises after the finding of photographs that were taken of The Smoking Man (William B. Davis) by X, false information is planted at the First Elder's behest, in order to root out the leak.
In the season 4 premiere episode "Herrenvolk", X's role as an informant is exposed, and suspicion arises after photographs of The Smoking Man (William B. Davis) are found by X. False information is planted at the First Elder's direction to uncover the leak.