For that reason Mark Olshaker and John E. Douglas are not characters in Mindhunter. Instead, Jonathan Groff and Holt McCallany play fictional agents in the FBI's Behavioral Science Unit, both only loosely based on Olshaker and Douglas. The series is set in 1979, but time is compressed, accelerating to get right into the action of the characters interviewing imprisoned serial killers. "This was an approach to really excavate the idea of a particular moment in time, which probably took eight years [in real life]," Fincher noted. "In the first two episodes they begin to get on their feet. [Joe]’s notion was correct: We can’t be bootstrapped to the footnotes. We have to be able to show the audience what they need to see when they need to see it in order to understand."
The killers represented on the series are, generally, based in reality. The first several episodes include interviews with Edmund Kemper, a serial killer who murdered his grandparents, mother and several young women in the 1970s. Douglas interviewed him in a California prison, where he is still serving several life sentences, and those conversations are reenacted for the purpose of the narrative in Mindhunter. Charles Manson and the Son of Sam are also included. These actual criminals, who existed in the public consciousness around the same time as Watergate, are a way for Fincher to look at the historic development of the FBI and criminal profiling in the context of a fictionalize tale.
"They realized they didn’t understand modern-day criminality," Fincher said. "Out of the basement grew this program of trying to sit with the most depraved minds that you could find to have them explain ‘What was going through your head?’ You had to acknowledge that your enemy was human and there were things about him we didn’t understand, but if you could empathize with him he might let you in on it. That was an interesting notion. That was intriguing to me."