Damon Herriman, who plays Charles Manson, also plays Manson in Once Upon a Time In... Hollywood (2019).
Academy Award-winning makeup artist Kazu Hiro (Die dunkelste Stunde (2017)) spent hours modeling actor Damon Herriman's face to best resemble Charles Manson for his brief appearance in this one episode. The actor's cheekbones and brows were prosthetically reshaped and a wig, beard and contact lenses were added to complete the sinister character. The swastika between his eyebrows is barely visible during the scene, even though it is on back to front.
When Tench and Holden arrive to talk to Ed Kemper, he is recording an audio book. In real life, Kemper spent over 5000 hours recording books for the blind, stopping only after suffering a stroke in 2015.
In the scene where Holden interviews Tex Watson, the ambient background noise mirrors Tex's speech as he describes the murders. He mentions being out at night and there are cricket noises. Twice, he mentions pulling a gun's trigger and a heavy bangs occurs in the background. After declaring that he is a born again, church bells ring. Upon describing the chaos in the house, there are sounds of schoolyard screaming.
The shot of the San Francisco airport entrance is actually an entrance of Monroeville Mall near Pittsburgh, PA, most famous as the primary shooting location for the 1978 film Dawn Of The Dead.