The discovery of the bodies in Cromwell Street, Gloucester, raises the perennial question posed whenever gruesome crimes in a household are found out - what about the spouse? Did Rosemary West know about the women buried in her garden and cellar? Was she involved? Did she collude by silence, or was she truly unaware of what was going on?

Frederick West has been charged with murdering nine women, but Mrs West denies involvement in any of the events. Her solicitor said she is 'very distressed, as it is an unprecedented and unimaginable situation to be embroiled in', especially since one of the victims is her daughter. She has been arrested twice, but so far no charges have been brought because of insufficient evidence.

We shall see. In such cases it would be the exception rather than the rule for the wife to be aware of, let alone take part in, her husband's crimes. Most of us could only come up with one example: Myra Hindley.

For my book Women Who Love Men Who Kill (True Crime pounds 4.99), I interviewed 13 women whose men had been involved in murder, and many more with violent partners. I discovered that time after time, when men are arrested for appalling crimes, the people most convinced of their innocence are their wives and mothers.

Shirl Marshall runs Aftermath, a charity that offers assistance to relatives of violent criminals, and has counselled many people, including the parents of the boys who killed James Bulger. In her experience, 'people do not know anything'. She gave an example of a young man who battered his elderly neighbour to death. His mother, with whom he was living, said she noticed no difference whatsoever in the behaviour of her son before or after the murder. She found it difficult to believe he had done it.

I also interviewed a woman whose mother had been killed. The mother, 24 hours earlier, had told her husband that she had a lover and would not sleep with him again. The father has now served six years in jail and only now is his daughter beginning to believe his guilt; but she needs him to admit to the crime before she will be totally convinced.

Two mothers I also spoke to, whose sons had confessed to murder, were both initially certain that they had been set up by the police. Neither could believe their sons were capable of killing.

It could be argued that mothers and daughters have a rather blinder faith than wives. After all, we choose our husbands, so surely we must begin to suspect when they act strangely. Ms Marshall considers this argument 'absolute rubbish'.

'People who have not been through something like this have no idea. Men who are serial killers have a certain madness,' she says. 'I say a certain madness because part of the person behaves normally. They are unable to express the madness in any other way. The rest of the time they appear to be normal.'

Ms Marshall has also counselled women whose husbands sexually abused their children. The first few sessions are often spent with the women berating themselves for not having seen or even suspected that anything was wrong. The truth is that they could not conceive of such a thing happening.

How many women, therefore, can suspect their husbands of deliberately killing one person - let alone systematically disposing of a number? Even those women who marry men that have already committed murder are certain that it will never happen again. I spoke to several who had fallen in love with men serving life sentences. All were certain they had married a changed man, a man who was no threat to anybody.

Each one felt their man's killing had been a one-off, that they were no more likely to kill again than anybody else. In each case I left persuaded - the men they described, or whom I had met, did indeed seem completely harmless.

Almost every woman I spoke to tried to rationalise the killing committed by her father, brother, husband or son. They were one-off incidents committed under provocation or there were extenuating circumstances. Murderers are not a race apart. It might be a more comfortable world if they were.

Except for their crime, however, nothing sets them apart from other, ordinary people. The men whose wives, daughters, sisters and mothers I interviewed had shown no predisposition for cutting up frogs or torturing puppies. I heard no reports of domestic violence before the murder; not even concerning the man who stabbed his wife to death.

Of course, while extenuating circumstances might explain one killing, a mass murderer is deeply disturbed. However, he still says hello to his neighbours and probably is kind to his Mum. Most of his life is unsuspiciously ordinary - even to his nearest and dearest, who also become his victims, for the guilt they suffer as a result of their ignorance is enormous.

One woman I spoke to had turned her brother away when he came to her for help about his marriage, because she was working. Days later he killed his wife. She is still convinced she could have stopped him if they had talked.

Sooner or later Mrs West will have to come to terms with the reality of her marriage. The difficulty of that will certainly be matched by the exposure of her private life. Already her brother and his family have had to move house to escape the verbal and physical abuse aimed at them because of their, at best, tenuous links with the killings. They are being punished for being relatives by marriage.

If her husband is found guilty, Rosemary West will, like other partners, be haunted by the crimes of 25 Cromwell Street for the rest of her life.