>

Goering was also hardly the only Nazi testifying at Nuremberg. His testimony, while valuable, was not invaluable anymore, there were lots of Germans present to corroborate or deny many of the things he had to say.
This guy's testimony may, at the moment, be invaluable. Not that it should matter too much, Norway doesn't have a death penalty and won't extradite anyone to where they would have a death sentence.
Curious to know if he has any interesting intelligence on Russia's strategy. >

Ukraine is saying he witnessed war crimes >

Probably perpetrated a few too. >

He's more then likely asked for immunity in return for Intel. 
However it should be noted that in Herman Gorring gave up a ton of info to the allies after the war thinking he'd receive immunity but was still sentenced to death for his part in the war.