Translation:There was no doubt as to who was responsible.
Of course it can't but in norwegian it seems there are actually two "whos" hvem and som. That's why I was asking.
Oh I didn't see that... However 'som' could still not be skipped. This cannot be explained in a very simple way, but I can give you some examples:
Det er han som løper = It is he who runs
Vi vet ikke hvem som løper = We don't know who runs
Alternatively the sentences can be rephrased.
Det var ingen tvil om hvem det var som var ansvarlig.
There was not doubt as to who it was that was responsible.
By your explanation I think the English translation can be: there was no doubt about who was responsible. Right?
It sounds like perhaps 'hvem som' might be loosely translated as "s/he who", but not the grammatical subject? Like in the accusative maybe?