I'm SO SAD that the book Citizen X is based on appears to be largely out of print and only available for outrageous prices on Amazon; I would love to do the background reading, but finding comprehensive sources on what went down crimewise in Soviet Russia is so hard. (For . . . obvious reasons.)

Have you watched To Catch A Killer? That one's about John Wayce Gacy, but it's also super interesting and has Brian Dennehey as Gacy (apparently Gacy wrote him a very indignant letter afterwards) and Michael Riley as Joe Kozenczak aka The Angriest Mustache of All Time.