"The Thin White Line" draws inspiration from real killers Herbert Mullin, Lawrence Bittaker and Roy Norris, and contains several references to Morgan and Wong's previous series Space: Above and Beyond.
Millennium Group consultant Frank Black (Lance Henriksen) visits a Seattle hospital to pick up his wife Catherine (Megan Gallagher), who works there as a counsellor.
Black and Bletcher review security camera footage of the crime, which leads to them discovering half a playing card—the Jack of Spades—at the scene.
Hance was a disturbed Vietnam War veteran who marked his kills with half a playing card, a custom he picked up during his tours of duty.
Meanwhile, Tyler calls the police and leaves an anonymous tip, telling them that the liquor store murderer is hiding in an abandoned building.
"The Thin White Line" was written by frequent collaborators Glen Morgan and James Wong, and directed by Thomas J. Wright.
[7] The relationship between the characters of Jacob Tyler and Richard Allen Hance seems to have been based on that of Lawrence Bittaker and Roy Norris, two convicts whose time in prison together formed the basis of a partnership that saw them torture and kill several young women in 1979.
[9] The character also draws inspiration from American serial killer Herbert Mullin, who likewise felt that his victims had offered him permission to kill them.
[12] The episode contains several references to Morgan and Wong's short-lived series Space: Above and Beyond, which had been cancelled prior to the pair joining Millennium.
Gibron noted that "with a stellar final act and a closing scene that has a great deal of impact in a very restrained manner, this is an excellent installment [sic]".
[17] Robert Shearman and Lars Pearson, in their book Wanting to Believe: A Critical Guide to The X-Files, Millennium & The Lone Gunmen, rated "The Thin White Line" five stars out of five, noting that "it's a return to the serial killer format, but it's never been done before with as much verve as it had here".