Actor Cameron Britton played Ed Kemper so well that he even started to think like the serial killer.
Britton played the prolific criminal in the hit Netflix series Mindhunter, and went on to be nominated for a Primetime Emmy for his role.
The real-life Kemper murdered eight people - his own mother included - between 1972 and 1973.
While he killed his mother, most of his victims were female college students that he didn't know.
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A lot of his murders included necrophilia, decapitation, and dismemberment, and he was later sentenced to eight concurrent life sentences.
Now 74-years-old, Kemper remains in custody at California Medical Facility and has been denied parole several times.
With his heinous crimes in mind, undeniably playing the serial killer will have been a difficult role to play.
Britton said he 'was in Kemper's head' for nine months and it certainly had an effect on him.
Like many actors who method act have experienced, Britton found he started having 'dark thoughts'.
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"I was in that dude’s head for nine months," he told Vulture in 2018.
"I honestly, I enjoy acting so much that endorphins are released when I’m performing.
"And yet I’m using a lot of dark thoughts to get where I need to go, so then dark thoughts become synonymous with endorphins.
"So my body just Pavlovian style starts wanting more dark thoughts even when I’m not shooting."
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Britton went on to recall a meeting with his mother that left him 'in tears' after he found he was having thoughts about killing her.
"When she left, I was in tears, she left and I said ‘bye mum, great seeing you'," he said.
"The door shut and I was like... It wasn’t me wanting to hurt my mum but the character who just can’t stand his mother."
Mindhunter was a hit with Netflix viewers, but it was never renewed for a third season.
The second series came out in August 2019 and director David Fincher has since confirmed that a third season won't be happening.
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"I'm very proud of the first two seasons. But it's a very expensive show and, in the eyes of Netflix, we didn't attract enough of an audience to justify such an investment," Fincher told Forbes last year.
"I don't blame them," he went on.
"They took risks to get the show off the ground, gave me the means to do Mank the way I wanted to do it and they allowed me to venture down new paths with The Killer."
But Mindhunter fans have remained hopeful - even creating a petition to have the show renewed.
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At the time of writing, almost 90,000 people have signed.
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