There has been an immense concern in recent years over the scale of child sexual abuse. But even after years of studies and investigation, there's still disagreement over what causes pedophiles to be the way they are.
'People, they think 'why should we help the pedophile? We should be prosecuting them, throwing them in jail, having them castrated'. But if we offer help to pedophiles we might save children who might have been abused.'
These were the remarkable words of Paul Jones, father of April Jones who was abducted and murdered by a pedophile in October 2012.
There was evidence that Mark Bridger had been looking at child pornography online in the hours leading to her abduction.
Now Paul and his wife Coral are campaigning for a better understanding of child sex abuse - including offering help to pedophiles to prevent them from offending. For them, this is key to protecting children from harm.
Dr. James Cantor, of the Centre for Addiction and Mental Health in Toronto, Canada, spends much of his time exploring the brains of pedophiles using MRI scans. He has reached a startling and controversial conclusion.
'Pedophilia is a sexual orientation,' he says. 'Pedophilia is something that we are essentially born with, does not appear to change over time and it's as core to our being as any other sexual orientation is.'
Cantor found that the brains of the pedophiles he studied were wired differently to non-paedophiles - something he describes as effectively a 'cross-wiring' of the brain. 'It's as if, in these people, when they perceive a child, it's triggering the sexual instincts instead of triggering the nurturing instincts,' he says.
He also says that convicted pedophiles are three times more likely to be left-handed or ambidextrous than the rest of the population - and that they are significantly shorter than other convicted criminals.
'The more we can zero in on exactly what's going on and when it's happening, the greater chance of being able to prevent it from developing in the first place,' says Cantor.
But his theory diverges markedly from the other explanations of why pedophilia exists. A nature/nurture debate is raging fiercely among experts in the field of child sexual abuse.
A possible cause may be maternal stress or malnourishment.
For a long time, the dominant thesis was what Duncan Craig of Survivors Manchester - a charity for male survivors of abuse - calls the Vampire Syndrome. Craig defines this as 'the idea [that] if you'd been bitten by a vampire you'll go on to become a vampire. If you've been abused you will go on to become an abuser.'
Cantor's work provides an alternative explanation of how pedophilia develops.
The debate is complicated by the fact that not all child abusers are regarded as pedophiles in the traditional psychiatric use of the term.
Many are what are termed 'hebephiles.' Where pedophiles are defined by a persistent attraction to pre-pubescent children, hebephiles have a very specific attraction to pubescent children, aged roughly 11-14. The character Humbert Humbert in Vladimir Nabokov's novel Lolita is perhaps the most famous example of this type of child abuse. Cantor says the brains of such people differ from the rest of the population in the same way as pedophiles - but to a lesser degree.
It's believed that many more people have desires that they don't act on.
To add to the complexity, about a third of those who offend against children are other children or young people under the age of 18. Kevin Gallagher runs an intervention center for such offenders in Wales and stresses that they must be viewed very differently from adult offenders. With this group, he insists, nurture rather than nature is the key factor.
'Our young people will have been through very difficult and traumatic early childhood experiences,' says Gallagher. 'We're talking about neglect, trauma, attachment difficulties, poor parenting experiences that sometimes will have included sexual abuse in their own histories.'
'The vast majority of young people of whichever age who engage in maladaptive sexual behavior with other children will grow out of that or, with the right sort of support and intervention, are able to understand where that's come from, deal with victim work and move on from these incidents.'