BBC director Rebecca Harrison has revealed her terror after coming face-to-face with psychopaths in an American prison for a new documentary on what drives them and whether they can be cured.
She sat opposite child molester Mark Moye, murderer Ryan Klug and killer rapist Joshua Wright, who are all serving more than 100 years in Indiana State Jail for numerous horrific offences.
Her BBC Horizon documentary "What Makes a Psychopath", reveals the biological and psychological influences that lead to murder and child abuse.
But it was her discussion with another prisoner called Robert, which revealed the true extent of a psychopath's warped reality as he tried to unsettle her with a Hannibal Lecter-style appraisal of her own state of mind.
He also told her about how he attacked a prison guard aged 17 and left him permanently brain damaged, saying: "The back of your neck is the weakest spot on your body, so I hit him there".
Her chilling interview with the 17-year-old revealed what she described as a "charming mannerism" that sucked her in to the avid reader's past.
Robert told Rebecca of his love of books, his dream of joining the US Army and how close he was to his family.
The teenager then started to speak casually of his past offences and boasted about being able to 'read' people just by looking at them.
Describing her experience to the Daily Mirror she said: "I became terrifyingly aware of just how dangerous this man really was".
She then agreed to let him appraise he personality based on her appearance.
He told her: "You're on edge a little bit" ... "I'm not a threat." ... "You've got dark pants on; you've got dark boots on.
"Your boots alone are laced all the way tight and your pants are darker of a colour, so you started today with a firm, determined goal....
"Your shirt is ... more at ease. It's not a hard colour, its see how the day takes me, I'm going to do this but we're just going to see how it goes."
Describing what happened she said: 'When I finally asked Robert if he thought he was a psychopath, he answered: "Narcissistic maybe. Not a psychopath."
"And with the American prison system unable to diagnose every inmate, we'll never know for sure. But I know what I thought".
Rebecca said the interview certified in her mind what the American prison system struggle to diagnose in 'every inmate'.
The Horizon documentary maker and her camera crew went to Indianapolis prison after "months of negotiation" to find out the answer to the question; what makes a psychopath?
Her interviewees were all chosen by the prison psychiatrist and she spent weeks in total speaking to them.