The BTK Killer has been a part of Mindhunter's DNA since the show's beginning, but Season 2 starts to actually bring him into the focus of Mindhunter's main characters. Since Season 1 the show has been peppering in brief vignettes of Dennis Rader's day-to-day life, from attempted murder to self-asphyxiation, but no one actually says the name "BTK Killer" until he ends up in crosshairs of Holden Ford and Bill Tench. In Season 2, the duo is just beginning their investigation, but the BTK Killer is still in jail today, per The Daily Mail. Viewers likely won't get to see how Rader is caught, unless Mindhunter decides to change history.
Mindhunter is set in the late 70's and early '80s, and in between all of the interviews of other serial killers, it also shows Dennis Rader's actions leading up to and following his failed attempt to kill Anna Williams in 1979. While Holden and Ford are made aware of BTK's actions in the season's second episode, Rader would not be found guilty of his crimes until 2005 when he confessed to ten counts of first-degree murder. While there's always the chance that Mindhunter could jump ahead 25 years and depict Rader's confession and sentencing, it's likely that Mindhunter won't show the BTK Killer getting caught and that Rader will remain on the fringes of Mindhunter's plot for some time.
Today, nearly 40 years after the events portrayed in Mindhunter, Rader is now 74 years old and is serving 175 years in prison at El Dorado Correctional Facility in Prospect Township, Kansas. In 2019, he send a letter to The Daily Mail to speak on his living conditions in prison, and reveal some chilling details about his last few years outside of prison — including his plan to perform a "retirement kill" before being caught. He wrote that he feels "very safe" at El Dorado and called himself the "facility pet." Rader claims that he has access to "TV, radio, hot-pot, books," and that he "can call people, have visitors, just live alone."
Rader's lengthy letter touches on everything from Turner Classic Movies to President Trump — but he doesn't make mention of his high-profile portrayal in Mindhunter Season 1, in which he is credited as "ADT Repairman" for the duration of the season. It's possible that Rader either isn't aware of his depiction, doesn't have access to Netflix, or simply didn't want to bring attention to the show.
Mindhunter Season 2 juggles multiple cases alongside the hunt for the BTK Killer, and sadly fans watching the series who have kept up with the real BTK Killer know that Holden and Bill aren't going to find the killer they're searching for for a long time.
While they may reach a conclusion in the case of the Atlanta Child Killer after a few years, as the police did in real life, Bill and Holden won't have an answer to the identity of the BTK killer for another quarter-century. The BTK Killer may be in jail today, but the road to put him there is long, confusing, and tragically marked by the deaths of multiple people.