***Warning: this article mentions sexual abuse.***

Robert Maudsley is the longest serving prisoner in solitary confinement in the UK and he will never be released.

Considered to be one of the most dangerous prisoners in the country, Maudsley is locked underground in a glass box in the Category A prison HMP Wakefield, sometimes known as 'monster mansion'.

A serial killer, Maudsley's first murder was in 1974 when he killed John Farrell, who had picked him up for sex and showed him evidence of child sexual abuse.

Maudsley was sent to Broadmoor Hospital after turning himself over to the police and telling them he needed psychiatric help.

While there, he and another inmate tortured and killed David Francis, a child molester, which resulted in him being transferred to Wakefield where he killed another two inmates.

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Since then, he's spent over 40 years in a specially built cell from which he's not allowed to leave.

His contact with the outside world is limited and recordings of his voice are incredibly sparse, though there are a few pieces of audio which are available for people to listen to.

Some of those come from interviews Maudsley did with psychiatrist, Dr Robert Johnson, who had been visiting HMP Wakefield when he developed an interest in the man they wouldn't let out of solitary confinement.

Conversations between Dr Johnson and Maudsley provide some of the few recordings of the serial killer's voice, including him talking about himself and his motivations.

In one of them, he appeared to be speaking about confronting the things he'd done in his life, including the series of murders he committed.

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"You see the thing is Bob, well I say I know, I know in the past I've tried to sort of face these things you know I'm just capable of doing anything Bob, as the adult here," he told the psychiatrist.

"And that's why I've got to be cautious Bob, you know?"

In other pieces of audio, Maudsley can be heard telling Dr Johnson he felt he had been making progress because the psychiatrist had 'come more into the room with me', and felt he was 'able to talk about a lot more things today than six months ago'.

While the serial killer was over time able to speak more with Dr Johnson, he will not be allowed out of prison.

Maudsley had in the past asked if he could be given a pet in his cell and promised not to eat the animal, while on another occasion he asked the prison to either give him a TV so he could learn about the outside world - or give him a cyanide pill so he could end his life.