The prosecutor actually shook hands with Brevik because that's how they always do it and the hell some mass murdering bastard is going to make them give in and change their ways for the worse.
...Is almost certainly the correct answer.
We've managed to take principled stands against things like paying ransoms to hostage takers for years, recognising that even though the consequences in an individual case may be horrible it is important not to lend any credibility to the strategy of taking hostages.
Today we are seeing a few very small groups of people, who want to instil fear to promote some sort of ideological position, who actually do relatively little damage but do it in ostentatious ways to seek attention. How is it that our political leaders and media reporters think the correct response to this strategy is to give these people exactly the attention they crave, with wall-to-wall graphic media coverage and inflammatory political statements full of phoned-it-in remorse and concern? If we want to disrupt people who support terrorism, perhaps we should start with all the influential people who are making terrorism a viable strategy in the first place.
I'm pretty sure the correct reaction to these kinds of incidents is to allow the police to investigate, to put the perpetrators on trial, and in this case probably to send them to prison for life like any other murderer. Meanwhile, the politicians and media could spend their time promoting (both politically and with funding) things like medical research or safer driving, either of which has the potential to save many more lives in a single year than preventing every terrorist attack that has occurred in the same places in my entire lifetime.