He very likely won't ever get out. He is allowed to have his case reviewed after 21 years (as it's how life in prison works in some European countries such as Norway, Sweden and Germany, not sure about others) but realistically he will never be out even if he's reformed as it will be a danger for his own life if he is back into the general population.

UK as well: https://en.m.wikipedia.org/wiki/At_Her_Majesty%27s_pleasure

He won't.

Norwegian law opens for in essence indefinite terms for inmates deemed a lasting danger to society.

ABB was sentenced under this statute and may well be locked up for the rest of his days; he may, however, at regular intervals apply to a board for release. He must then convince this board that he is no longer a threat to society and good luck with that.

I remember there being some amount of objection to his freedom to communicate while in prison (sending letters espousing his ideology, and such). Although this evidence of his continued ideology will probably help ensure he isn't released.

Hard cases make bad law.

Focusing on what (to you, as an outsider) seems to be outlandish is honoring the breach rather than the observance.

And unlike, say, the United States--there's only been one of him. This country has folks trying for high scores on a very regular basis. (Remember Las Vegas? That was 18 months ago. 59 deaths.)

Perhaps it is worth looking at trends and impacts rather than media splashes.

Not at all, he'll be way beyond the age window where men commit violent crimes. Old age mellows.

He'll also be under close supervision.

He'll be in his early 50s. I know plenty of men at that age that could crush me regardless of what statistics say otherwise.