When you are married to your business partner, it is difficult to leave your work at the office. But when your business is murder, it is a skill worth learning, says Adam James.

Rebecca and Russell Dobash have murder on their minds every day. But there is nothing macabre in this - it is just that the American-born husband-and-wife team from Manchester University are conducting Britain's most extensive study of murderers.

Over the past 18 months, the two professors at the university's department of applied social studies have been travelling England and Scotland to interview paedophiles, hit men, armed robbers and other killers serving life sentences. They have gone into prisons to hear 200 male and female killers describe, sometimes in grim detail, their lives and the act of murder itself.

Preliminary results from their report, Homicide in Britain: Risk Factors - Situational Context and Lethal Intentions , are to be published in journals and presented at conferences during the coming months.

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Many might flinch at the prospect of a tete-a-tete with those who have committed such violent acts. But violence is a facet of human behaviour the Dobashes are not only familiar with but, through experience, are also remarkably comfortable with. For more than two decades, domestic violence has been their specialist field. They have written five books on the subject, and they helped set up Scotland's first women's refuge.

Their 1992 publication Women, Violence and Social Change won the American Society of Criminology's Distinguished Book Award for comparative research. They have also been given the American Criminological Association's August Vollmer award.

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"We are working in the misery business. Some days we ask ourselves why we do not study holidays," jokes Rebecca. She is a professor of social research and, with her husband, co-director of Manchester University's Violence Research Centre.

"But we are social scientists," emphasises Russell, a professor of criminology. "We do not sensationalise our work. It is not like a Tarantino film."

This detached professionalism prevailed throughout their investigation, funded by the Economic and Social Research Council, into what motivates people to kill. It helped the pair to conduct the unique quantitative and qualitative research they hope will offer strategies on how to prevent homicides.

First, they had to pore over case reports written by police and prison officers, psychiatrists, social workers and judges on 1,000 murderers. The information they extracted was added to an extensive database.

Second, after being granted Home Office permission, they interviewed the murderers. With each, they discussed:

• Childhood, family and school life
• Their first offence
• Life circumstances at the time of the murder
• Details about the act of murder and about what happened immediately afterwards - did they hide from the police, and how were they traced?
• Life in prison, and any participation in rehabilitation or education programmes
• The effect prison life has had on them.

Although they will not speak about their results yet, they will reflect on the meetings. Russell says: "It was important for us to personalise the exchange. To make it like a conversation. We would shake hands and help them (the murderers) feel relaxed. They would often feel more relaxed than we did. Some have already talked a lot about their offences."

The couple are hardened researchers and conducted the job professionally. Yet they admit to having occasional nightmares triggered by their work. "You can never completely distance yourself from the things you read and hear about - and neither would you want to. There was always a sense of anger, horror and desperation about what we read and heard," Russell says.

"Although you cannot be desensitised by the experience, if it ever happened that we became overwhelmed by our work we would have to stop," Rebecca says.

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Her husband adds: "We would discuss cases afterwards. That was our catharsis."

Of all the cases they became familiar with, it was, unsurprisingly, the stories of those who had killed children that troubled them most. "While it was sometimes hard for them (the child murderers) to say what they did, it was also hard for us to hear it," Rebecca says.

"It was not during the interview but afterwards that we reacted to what we heard. It was on the train on the way home that I would feel very tense and my body would ache because of what we had been hearing."

Because of confidentiality, the Dobashes cannot discuss individual cases, even anonymously. But it was inevitable that they formed opinions about the killers they interviewed and had a range of reactions to their crimes. As well as the horror, there was astonishment. Like, for example, learning how hit men would take someone's life for just Pounds 2,000.

With other murders they felt puzzlement. For example, why did one member of a violent couple not have the foresight to end the relationship before it got to the point where, in either blind rage or premeditated revenge, one stabbed the other to death?

And then there were the unnecessary, mindless killings. Like when two alcohol-fuelled young men would fight outside a pub on Saturday night and one would end up dead with a knife in his chest.

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"Instances such as these were distressing because they were avoidable. And then you would learn of the horrendous childhoods some had. You just felt they were sad cases," Rebecca reflects.

Yet, despite being able to afford sympathy for some of the prisoners' predicaments, they were frustrated with others.

Although the Dobashes never once felt intimidated during interviews, they were infuriated by the "self-obsession" of some killers.

"Sometimes I would get very impatient," Russell remembers. "Some of those guys are extremely obsessive and self-oriented. It was hard to get them away from talking about themselves. The crime was always someone else's fault and responsibility. For some, it was a struggle to get them through the interview. Rather than an exchange, the interview would become their monologue. They would always return to the same subject, perhaps how they felt persecuted by the prison service."

They may not publicly discuss individual cases, but where is the cut-off point? Not only do they live, sleep and eat together, it only takes one of them to walk a few paces down the corridor to reach the other's office. On top of this they share an intellectual interest in murder. Is it not all too intense? "We do have rules," asserts Rebecca, insisting they do not work 24 hours a day.

"There is, of course, a possibility that our entire lives could be consumed by our work, and we could spend the whole time talking about it. But we try to have one day a week when we do not work. Instead we will go shopping, do some gardening or go to the movies."

Yet, one gets the impression that, for these two dedicated social scientists, even this self-censorship is a strain.

They admit that at home they will enthusiastically start discussing pressing issues that their work brings to light, or their competing interpretations about what motivates different types of killers.

"Murder is an interesting intellectual problem," Russell says. "And we may be watching television when a killing is mentioned. We will discuss how it relates to what we have seen and heard."

Sometimes they will also read or watch a murder report involving someone they visited in prison. The most recent was a docudrama about the sexual abuse scandal in children's homes in North Wales. One killer they interviewed was an abuse victim from one of the homes.

However, if there is one enduring effect on their lives from their research, it is a heightened sense of being vulnerable.

Many of the murders they have learnt about evolved from relatively everyday events - like burglars who, if disturbed and caught red-handed, would assault the person who found them, leaving him or her dead.

"I know that murder is statistically a rare event," Rebecca says. "But, from our work, we saw how ordinary events can turn into quite extraordinary ones. This is what horror films are about - turning the ordinary into the extraordinary. Alfred Hitchcock did this with films - when having a shower or seeing a flock of birds became something horrible."

VIOLENCE AND ACADEMIA

Manchester's Violence Research Centre was set up in 1995 as a "loose federation" of international researchers and academics working predominantly in the field of domestic violence, but also covering homicide.

Research includes a report by Sevaste Chatzifotiou on the first battered women's refuge in Greece, opened in Athens five years ago. Plus the first survey of the extent of domestic violence in Spain.

The Dobashes have conducted research into the effectiveness of cognitive-behavioural therapy programmes in changing the attitudes of males convicted of violent offences against women.

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A book on their research, Changing Violent Men , will be published by Sage later this year.