As more and increasingly disturbing and baroque details emerge within a confession issued by Josef Fritzl from his prison cell, who imprisoned his daughter Elisabeth beneath his home for 24 years in a specially designed cellar, and whom he repeatedly raped and who subsequently bore seven of his children between 1992 and 2002, there will be a temptation to simply consume these details as "true crime", shake one's head in appalled disbelief, but not really understand what might have propelled Fritzl on this bizarre and awful journey.

And, while I have read and heard a great deal of speculation about his motivation - from the unique nature of Austrian culture, to more individualised analysis - and about the behaviour of other family members (most obviously, Elisabeth's mother Rosemarie - did she know or not?), much of this analysis has been based on little direct testimony from Fritzl himself. Instead, it has been generalised from accounts of survivors of what are seen as similar experiences, such as Natascha Kampusch and Elizabeth Smart.

There are obvious cultural links to the Kampusch case - Natascha was abducted in Austria in 1998 and imprisoned by her abductor for some eight years before escaping - and to the equally bizarre circumstances surrounding the kidnapping of Elizabeth Smart, who subsequently lived with her abductors in Utah for nine months and who was often seen in public with them, but disguised behind a veil. But there are notable differences, too. Most important of these is the fact that while these abductions or kidnappings were extra-familial, the Fritzl case is very much intra-familial. So, we need to understand the Fritzl case not from the perspective of, for example, hostage-taking and the Stockholm syndrome, but rather from what we know about incest, domestic violence and trauma bonding, and Fritzl's confession offers us one way to see what it is that drives this type of abuser.

In his confession, Fritzl explains that he "had to create a place where I could keep Elisabeth by force if necessary, away from the world". In short, he created a parallel universe - "a place", which we now know was a locked, three-roomed cellar in his house, and in which he was the lord and master. He controlled who lived in this place, what they ate, how they got access to heat, light, water, and, of course, this control facilitated his desire to sexually abuse his daughter.

The phrase "by force if necessary" is of interest, too, because the reality would be that with the control that he exercised within this parallel universe - this dark hole which no natural light could penetrate - force would not have been necessary, especially after any initial attempts to escape (if there were any), since he would have been able to convince Elisabeth by bribes and threats that this universe was all that she would ever have access to. In this respect, as Cath Elliott has argued, Elisabeth is similar to all those women who, for years, put up with abusive partners and husbands, and who never felt able to leave those relationships and might also hide their bruises and black eyes and broken bones. In this respect, Elisabeth is also similar to the children of Fred and Rosemary West who became convinced that the only world that they would ever know would be Cromwell Street in Gloucester, where they were routinely sexually and physically abused for the pleasure and entertainment of their parents.

Of course, that was what Fritzl wanted, too - to use Elisabeth sexually - and, as he says in his confession, he could no longer suppress his "desires" and "my desire to have sex with Elisabeth became ever stronger... it was a vicious circle from which there was no exit." This, again, is an interesting statement which both returns to the issue of place - from which there was no "exit" - but also pushes our understanding forward in relation to the overwhelmingly sexual nature of what Fritzl was trying to achieve within this place.

There is special pleading going on here, too, because he is asking us to feel for him - the lack of an exit he is describing is about his own situation, rather than an exit for Elisabeth from the cellar - and his "vicious circle" is meant to engage our sympathies in the same way that we might sympathise with an addict or alcoholic. Of course, while addicts and alcoholics largely harm themselves, Fritzl harmed others - most obviously Elisabeth, but also the children she subsequently bore.

Again in his confession, Fritzl admits that he did not use contraception. This is also of significance because it makes clear that he wanted to have children by Elisabeth. In other words, not only was this a parallel universe in which he would be able to control his daughter, but also a parallel universe that would be populated after his - and her death - by their offspring. He was seeking to create a world that was absolutely in his image; a world in which he was God.

Is he mad? Elizabeth Smart's kidnappers - David Mitchell and Wanda Ileen Barzee - (the former of whom also had God-like delusions) have never been able to stand trial because they are seen by the courts as being mentally unfit to plead; and there are obvious and common-sense arguments to suggest that anyone who locks up their daughter for 24 years and repeatedly rapes her is not operating on the same moral plane as you or me.

However, immorality and madness, while they can be related, are not necessarily conjoined. It seems to me that Fritzl was more than aware that what he was doing was wrong - indeed, he says that "I knew what I was doing was not right" - and that he deliberately set out to create an appalling set of circumstances which he could exploit to have power and control. In that respect, he is no different to the rest of us and, as such, is sane and fit to plead. If the Smart case is anything to go by, however, there will be years of legal wrangling before any case might come to trial.