As a law student of the University of Oslo I think some things needs to be clarified here...
Basically the ground values of the Norwegian justice system is to get people back into society after they have served their sentence. We have two different types of prison sentences here i Norway, one is definite, as in you get so and so many years or months in prison, and you have to participate in activities designed to get you back into the society when your time is served. The other one is indefinite, meaning that you can be held in for as long as it is deemed necessary. This form of punishment is called "forvaring" in Norwegian, translates to
preventive detention in English. The whole idea behind this is to protect the society from dangerous people in cases where the defendant is likely to commit a serious crime again. You'll find this in the
Norwegian Criminal Law (Strl.) ? 39c
What Breivik got was essentially a 21-year detention sentence with a minimum time of 10 years which is the strictest they can give, see
Strl. ? 39e. Meaning that he can do nothing for the next 10 years, only then he can apply for a parole, but he is very unlikely to get it. There are prisoners at Ila Landsfengsel who have been locked up for 25 years without parole for less serious crimes than this... After 20 years he is supposed to be released (-1 because he has already served one year, in custody since July 22 2011), but three months before the release the Prosecutor can go on trial in the district court and demand five more years at a time, until the day he dies if it's deemed necessary.
So, no need to change any laws here... Also any change is laws would not make any difference as retro active laws are unconstitutional as per
Article 96 and 97 in the Norwegian Constitution. This is an important part of the principle of "
Rule of Law" on which the Norwegian justice system is firmly built.