So after the first time, he would have to feel so terribly that he frees them and ask for forgiveness
In some people, the empathy does not work properly (which may possibly see even in functional imaging).
This type of shame or he obviously did not feel remorse. I do not believe that such terrible people can measure with normal, emotional standards. Because then they would not have done something like that. On such ideas, a normal person would not at all.
I recommend the following article: https://www.spiegel.de/panorama/justiz/psychiatric-Vutachten -Josef-FritzL-suffers-an-heavy personality-a-585796.html
This is difficult to imagine from our perspective, but, Fritzl has simply due to its livesENS psychic problems that turn off the conscience the ordinary man has, in combination with a disturbed sexual preference.