Moors Murders viewers were creeped out as CGI brought killer couple Ian Brady and Myra Hindley's mugshots to life.
The documentary shone a light on the horrifying child murders that took place near Manchester from 1963 to 1965.
Viewers said they were "sickened" to see the vile murderers come to life in the Channel 4 show.
In the harrowing documentary, Clive Entwistle said how police discovered a suitcase which had a tape recording inside of a child being tortured.
It was this tape that snared monstrous Myra Hindley as she could be heard talking in the background.
She and her twisted lover Brady were jailed or three murders in 1966 before confessing to another two murders.
Hindley died in prison aged 60 in 2002.
Speaking of the recording, one viewer wrote: "The thing that chilled me most was the recordings they had. That poor lassie calling out for her mother and getting the brutal death she faced.
"All because she was alone, innocent and vulnerable to them."
Another added: "The tape recording has to be one of the most horrifying bits of evidence in British history, poor girl."
The CGI used on the mugshots was what chilled people to the bone, with one adding: "Those animated mug shots with the blinking eyes are freaky."
"I actually hate those moving mugshots...scum of the earth, making my blood boil," another wrote.
Segments from Hindley's unpublished diaries were read out in the documentary, which told a chilling tale of the pair's blood-thirsty ways.
Hindley, was hired as Brady's secretary at Milward's Merchandise when she was 18 years old. She fell head-over-heels for him and was set on pleasing him.
She documented the first time they met in one entry, where she wrote: "Ian wore a black shirt and looked smashing, I took him home and he was so gentle."
But in a separate entry she wrote: "He's a crude, uncouth pig. He's cruel and selfish and I love him.
The cold killer wrote: "I hope Ian and I love each other all our lives and get married and are happy ever after."
In her memoir where she appeared to try to pull at readers' heartstrings she penned: "At the age of 18 I met a man who convinced me there was no God at all.
"He could have told me the Earth was flat, that the sun rose in the west, that the moon was made of green cheese and I would have believed him, such were his powers of persuasion. I believed him because I thought I loved him."
In the documentary eyewitness David Smith said how he watched the sick couple murder Edward Evans with an axe in 1975.
He was just 17 at the time and was married to Hindley's sister Maureen.
"I was in bed late in the evening and the bell rings. I get out of bed, and there was Hindley."
He said: "Maureen gets up, thinking it's an emergency, but there's not, everything is fine."
He described how Myra asked him to walk her back home, before taking him into the kitchen.
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He said: "All of the sudden, there's screaming, there's swearing, there's banging around. She screams 'Dave, Dave help him!"
"I go running into the living room and Brady has this lad. It's very violent. Very, very violent."
