LONDON (Reuters) - More than a decade after Fred and Rosemary West were arrested for a string of grisly murders that shocked Britain, the man who brought the couple to justice still cannot shake the painfully vivid memories of what he saw.

For former Detective Superintendent John Bennett, the sights and smells that accompanied the discovery of bodies buried under the West family home at 25 Cromwell Street in the town of Gloucester in western England, will never fade.

"The word 'evil' continues to be used and although I detest using these types of word, there is no other. They were the epitome of evil," Bennett told Reuters.

"Even after all this time, it genuinely saddens me to think about it ... it is beyond belief what they did," the senior investigating officer in the case said, 10 years after Rosemary was jailed for life for the killings.

The tubby middle-aged housewife with a penchant for knitting was found guilty in 1995 of killing 10 women and girls, including her 16-year-old daughter Heather.

"They (Fred and Rosemary) were so detached. That is what is hard to comprehend," said Bennett, who went on to aid the Belgian authorities with the case of Marc Dutroux, who was convicted last year for kidnapping, raping and killing girls.

"How can anyone live a 'normal' life, having parties, barbecues going to the bathroom, knowing there are people, including your own daughter, buried underneath?"

For nearly 20 years, the Wests lured vulnerable young women to their Victorian terraced home in the quiet cathedral city of Gloucester. They tortured, raped and killed their victims.

Fred, a jobbing builder, would then bury their bodies in the cellar, under the bathroom or, in the case of Heather, under the patio in the back garden.

"The smell of body fats decomposing, once you've smelt it you never forget what it is," said the retired officer, who spent days at the West home.

The killings only ended in early 1994 when police renewed probes into Heather's disappearance seven years earlier. The search was partly triggered by comments made by some of her siblings when they were in temporary care.

"He maintained the stance that Rosemary did not know, right up until the very last interviews ... when he sort of suggested Rosemary might have been involved," he said.

Bennett believes this change of heart may have come about after police told Fred about Rosemary's sexual activities, which he did not know about.

Bennett's book -- "The Cromwell Street Murders: The Detective's Story" -- was written partly to counter some of the lurid accounts published shortly after Rosemary's conviction.

"Fred kept changing his story the whole time. He got a kind of enjoyment out of being questioned, about going off on tangents, drifting into lewd discussions about sex."

The brutal contrast between the West's public facade of a loving family and the reality of what went on behind closed doors is something many struggle to comprehend. Bennett's chronology of the Wests' lives chillingly illustrates this.

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