Until a stroke sidelined him in 2015, the real Ed Kemper was a prolific reader of books on tape, logging over 5000 hours narrating several hundred books.
Cameron Britton, who plays Ed Kemper, stands at 6'5 in reality but with the help of shoes, he does stand at 6'6 as his character is portrayed. The real-life Kemper stood 6'9" tall and, by the release of this series installment, was 68 years old and still incarcerated at the California Medical Facility, Vacaville (CA).
The Playboy in Bill's box is from April 1977.
The scene where Holden (Jonathan Groff) runs into a potential recruit at a library was filmed at the University of Pittsburgh's Hillman Library.