Taking Cromwell Street to Charing Cross Road

When Howard Sounes, 30, sits down to work on his book about Rosemary and Fred West, his feet rub against two mantelpiece dogs. "I took them from the house in which Fred West grew up," he says with relish. "I think they are rather fun." His girlfriend hates the statuettes and the rest of the West paraphernalia, too: photographs of the House of Horror victims, files of interviews boxed on shelves. The east London flat is pokey enough as it is.

Over in west London, Brian Masters, 56, author of a biography about the killer Dennis Nilsen, is also writing a book about Rosemary and Fred West. He lives alone in a prim, seven-bedroomed house ("bought it years ago when property was affordable"). Mr Masters doesn't collect Fred West artefacts, but, like Mr Sounes, he is obsessed with serial killers - not the detail about what they actually do but why they do it.

Mr Masters says his will be an analytical book, which he will only start writing once Rosemary West's trial has finished. The book will take the reader on a trip "which goes beyond mere voyeurism. It will allow them to rub shoulders with wickedness. It will open doors."

Mr Masters and Mr Sounes are just two of six authors producing books about Rosemary and Fred West. Others include Gordon Burn, famed for his book about the Yorkshire Ripper; Virginia Hills, a journalist at the Daily Star; and Gary Jones and James Weatherup, crime reporters at the News of the World. All will be the most avid followers of the trial of Rosemary West, Fred's wife, which begins in Winchester today. They are writing different sorts of books, but all cite the same justification for replaying in detail what went on in the West's house in Cromwell Street, Gloucester: they want to give their readers an understanding of what made Fred West a killer.

For centuries, writers have sought to answer the question of what motivates a murderer, with varying degrees of success. Some used parable, some poetry, others philosophy. Today's writers use legwork: cold calling relatives and friends of the killer, asking them to answer questions about childhood deprivation and traumas, teenage relationships and sexual experiences. Mixed in come "conversations" with police (anonymously, of course), quotes from psychologists and interviews with social workers.

The modern true-life crime genre, from the hardback pretensions of Mr Masters to the newsagents paperbacks of tabloid crime reporters, are the inheritors of a writing tradition that stretches back as far as 19th-century novelists. Is there any evidence that the exploding modern journalistic version of the genre is as insightful as the earlier attempts of novelists and philosphers? Is the author's quest to discover the truth at best wishful thinking and at worst impossible, simply a way of feeding the public appetite for gore?

Mr Masters argues that 19th-century novelists such as Zola, Dostoyevsky and Dickens had greater freedom. "They were able to collect observations and reflections and concentrate them into fictional characters. Today's crime writers have to restrict themselves to case histories." Novelists used their status as omnipotent, omniscient narrators to explain why someone kills; readers were prepared to accept their authority. Modern readers are not so accepting, they want evidence and proof; so the modern crime writer has to rely on the co-operation of the killer's associates to get information.

Yet readers a century ago were, arguably, more sophisticated. They were willing to engage in philosophical debate about the motivations of murder. They were encouraged to imagine their way into the killer's head and to engage in philosophical debates; was murder a response to a meaningless of life? Do killers have a greater desire to exercise free will or a more brutal nature? By contrast, the modern journalistic genre, however well researched, provides explanations in soundbites, personal history or pseudo science.

The source of that documentary approach to murder writing was probably Filson Young, a lawyer come author, who used real-life crime case histories as material for a book. In 1910, he wrote what is thought to be the first documentary-style book about murder. It was about the trial of Dr Peter Crippen, the north London doctor who poisoned his gregarious wife, Belle Elmore, so that he could elope with his mistress.

However, it is perhaps no surprise that the modern genre really began its life in America. It's creator was probably Truman Capote. In 1966, he wrote In Cold Blood, documenting the murder spree of two young men in America's Midwest. The book has since been criticised for mixing the true-life genre with the novel (the author is said to have described conversations that did not occur).

Capote's British equivalent came a year later with the publication of Beyond Belief, a book about the Moors Murderers by the actor Emlyn Williams, which is remembered as a cry of anguish rather than an attempt to account for the murders. It took Norman Mailer to give the genre distinction. The Executioner's Song in 1975 (the story of Gary Gilmore's fight to be executed) was a worldwide success. Mailer took the reader into the hows and whys of murder rather than restricting himself to describing events.

Few modern murder writers match Mailer's standards because if the task is approached seriously, it may be difficult to complete. That is what Emma Gilbey, a freelance journalist, found. In February 1994, she was asked to write an in-depth explanation of the gruesome happenings at the House of Horrors. Ms Gilbey accepted the advance, thinking that interviews with the family, friends and perhaps Fred West himself, combined with some sociological and psychological analysis, might yield some answers. Three months later, she gave up: the brief, she found, was impossible to fulfil.

"I thought it would be possible to understand Fred West by looking into his family, his background," she says. "But the fact remains that if you were to put somebody else into that family setting, he or she would be unlikely to commit such a crime."

What made her decision to give up all the more incredible to other writers was that Fred West had contacted her through his social worker, offering to work with her on the book. This is every author's dream. Yet it was Fred West's offer that convinced Ms Gilbey that the quest for the truth would never be resolved.

After seeking professional advice from experts at the Behavioural Science Unit at the FBI, she was told that Fred West would never be "totally honest". His motive for talking would be self-titillation: he would enjoy the thrill of reliving the experience by watching Ms Gilbey's reactions. It was then that she decided to abandon the book. "It is a decision I have not regretted," she says.

Her sensitivities do not impress Mr Sounes. "Anyone who says they don't want to write about the West trial must be bananas," he says. He thinks his book explains Fred West's motives - with the help of numerous interviews with people involved. "Finding out the truth has been my quest," he says. He hopes he has got it right: "I don't want to be seen as a fool."

Mr Masters is more sympathetic to Ms Gilbey. "Yes, there is an X factor which may be difficult to identify ... but it is the job of the author to make coherent and intelligent suggestions about what that factor might be."

Much of it, he admits, is guesswork. "No writer worth his salt will announce that he has the answer. But the important thing is to ask questions in an attempt to find the answer. One must not give up because it is difficult. One must try to tease out an explanation, even though the answer may be buried and not obvious from the facts."

This "industry", this trick of turning other people's lives and misery into a product for the market, was another reason Ms Gilbey decided to abandon her book: "I didn't want to write a book like that would end up on a book table in a shop surrounded by lots of other books on the same subject. It felt disgusting ... horrible like we were cheapening the whole thing," she says.

In order to answer the question about why West did what he did - and what impact this had on the families of the victims, Ms Gilbey knew that she would have to seduce the relatives of the dead women into sharing their grief with her. But when she confronted them for the first time, the experience made her doubt whether she could do it. "I have seen grief before, but I have never seen it like that. After the inquest, I drove up to London. Then I burst into tears. I couldn't stop crying."

The job didn't get any easier when the time came to learn about West's alleged crimes. "After a bit I found my emotions were becoming blunted. ... When friends asked me how I felt covering such a horrific story, I would say: 'Nothing. I feel nothing.' Yet this was supposed to be book which broke hearts, which caused a reaction. But how could I write it? I'd lost all sensation."

Mr Masters is understanding. "Some evidence is damaging to the psyche," he says. "It is hurtful. Troubling. Sometimes one feels it would be better not to hear it - even if it does throw light on the killer's character." But Mr Sounes says the story depends on the detail. He has made a point of detailing some of the more abominable scenes. "I have made a point of describing some of the scenes in a straight-forward, factual way," he says. "The Fred West story is so incredible that you can do it straight and it is still fantastic."