Season 3 Episode 21 - Avatar 

During a one-night stand in the midst of his divorce, AD Skinner becomes a murder suspect, and Mulder and Scully return the many favors that he has done for them by analyzing evidence that someone doesn't want uncovered to prove his innocence.
Keywords: x-files, mulder, scully, full episode, season 3, episode 21, avatar, 3x21