According to this article, Josef Fritzl (the Austrian man who kept his daughter in the basement for 24 years as a sex slave) will be undergoing psychological testing to assess his level of responsibility for his offense. According to his attorney, he will be evaluated by experts for this purpose at an unspecified date. From the article:
"The results of the psychiatric tests will influence how guilty he is deemed to be, and consequently, how long his prison sentence will be. Mayer said to the BBC "We'd need to see if there's evidence of any psychiatric disorder - which wouldn't necessarily mean mental incapacity but would still be very important when assessing the guilt of the suspect. And the extent of the guilt determines the extent of the penalty."
Obviously I'm not familiar with Austrian law, but based on the bit I've read about this guy, there is absolutely no evidence of any mental health issue that would rise to "severe mental disease or defect" that would interfere with his ability to "appreciate the nature, quality, or wrongfulness of his actions," which is what the NGRI ("Not Guilty by Reason of Insanity") defense requires in the United States. Here is a partial description of his overall functioning level, again from this article:
Josef Fritzl, aged 73, led a double life. People in the Amstetten considered Josef and Rosemarie as respectable members of the community. However, DNA tests have confirmed he had fathered many children with his daughter. According to the local police, he lured his 18-year-old daughter into a cellar in 1984, and abused her over and over again.
Fritzl is a qualified electrician and, according to the police, a very intelligent man. The cellar room doors were fitted with locks that only he, with a special code, could open. There was a sliding reinforced concrete door which only he knew how to open and close.
The article also mentions another piece of evidence that very much calls into question a lack of awareness of wrongfulness; he bought supplies for the hidden relatives in towns surrounding his own, never in his own town. This would most likely be suggestive of a desire to avoid detection (which demonstrates the aforementioned awareness).
In United States Federal Court, there is also something called "diminished capacity," which is roughly defined as, "I did it, but my mental health problems contributed to my behavior." Again, I don't know the details of this case, but I can't think of a mental health application in this case - he did this for 24 years. All relevant mental health issues are episodic in nature - over the course of 24 years, he would have had points of functioning with ample clarity, given his intellect, to recognize what he was doing and stop.
Hopefully, in addition to the sensationalistic stuff that is sure to dominate the news regarding this case, some information regarding how the Austrian legal system addresses mental health statutes will also find its way into the media.