Fritzl has already been sentenced.
Here is a more recent article regarding the case. If you cannot be bothered to read it all, to sum it all up, he has received a life sentence to be served in a mental institution. Should the doctors ever think him cured then he will serve the remainder of his sentence in prison.
He was charged with rape, incest and deprivation of liberty which he admitted, but at first pleaded innocent to murder (by neglect?) and enslavement. He changed the plea to guilty after his daughters video testimony was shown. He is also now being investigated in relation to four other murders.
He says he's sorry but his initial plea of innocent, in my opinion, shows that he is only sorry that he got caught.
I am firmly against the death penalty so I do believe that the sentencing was appropriate. The worrying thing is, as I understand it, he could be out in 15 years if he can prove he is not a menace to society.