The man who inspired Netflix's Mindhunter series has revealed why lie detector tests are no good when it comes to serial killers.
John Douglas was the FBI's first criminal profiler who conducted high-profile interviews with the likes of Charles Manson and Ed Kemper.
Manson was behind a series of brutal murders in 1969, including the killings of actress Sharon Tate and six others by his followers, the 'Manson Family'.
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While American serial killer Kemper was responsible for murdering 10 people, including his grandparents and mother, between 1964 and 1973.
Now aged 79, Douglas is a retired special agent who has opened up about his experiences chatting to some of the most horrifying serial killers of all time.
He wrote the book Mindhunter: Inside the FBI's Elite Serial Crime Unit which was picked up by Netflix and turned into a docuseries.
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Lifting the lid on what it was like speaking to criminals as chief of the National Center for the Analysis of Violent Crime, the New Yorker has explained why he isn't a fan of lie detector tests.
He told Masterclass: "Lie detector tests, I'm against them. I'm really against them. If you're thinking that people are going to respond like you respond, no way.
"In my experience, many serial killers like Ted Bundy and the Green River Killer have passed polygraph tests over and over again.
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"The theory behind a polygraph is when people are lying, they experience a different emotional state than when they are telling the truth. Their heart rate increases.
"They sweat more, or their breathing changes. These are all physical signs of anxiety that are difficult for the body to hide, but some people can."
Douglas continued: "One of the key factors with the psychopathic personality is really the lack of anxiety.
"They don't have the anxiety. Their heart doesn't race, you know, like yours would. But whatever the crime may be, they may feel it's justified.
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"And because they feel like the crimes are justified, they don't show these signs of anxiety and nervousness in a polygraph test.
"The other thing I don't like about with the polygraph is that, if you're doing an investigation, you're telling the person that you really don't have any information.
"Because if you had information, why the hell do you want a polygraph me? So I'm really-- I'm not in favour of polygraphs."
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You can stream Mindhunter on Netflix now.
Topics: Crime, Netflix, True Crime, Mindhunter
Anish Vij