Jack Erdie, best known for his roles in Banshee and Outsiders, plays Richard Speck, one of the more troubling serial killers that Holden and Bill come into contact with in season one. The crimes he relays to the FBI agents on the show match up with his real-life offenses, which included breaking into a dorm for student nurses in the '60s and brutally killing eight women who lived there. He also raped his last victim, Gloria Davy, before strangling her.
One woman, Cora Amurao, manged to escape by hiding under a bed while Speck left the room, so he lost count of how many women he was holding hostage and didn't realise she'd disappeared (something Holden and Bill discuss with him in the Mindhunter scene). Speck was later sentenced to death for his crimes, but the issues with jury selection led to the sentence being overturned. He was later sentenced to 400 to 1,200 years in prison and died after 25 of those years from a heart attack in 1991.
Image Sources:
Netflix and Getty / Bettmann