Great presentation of the complexities and shades of grey  in this subject. A prof I know, an emigre Hungarian, found out in the nineties that a grad student of his had informed on him. (The prof had left soon after the war following a session with the secret police for being a Socialist activist, he was subject to what the White House would call an aggressive interrogation. At the time of the informing he was involved with emigre Hungarian activities in the US.) The grad student was an American who had been threatened with being barred from the archives if he didn't inform, so he did, instead of trying to get advice on how to deal with the pressure. The secret police were looking for dirt on the prof's private life and on his friends in Hungary. He had the gall to ask the prof for a rec after the spying had come out - needless to say he did not get it.

A couple friends of the family in Poland informed - they ranged from people who broke one time under interrogation  and didn't cooperate afterwards to scumbags who eagerly volunteered for privileges and favours.  As you say, quite a range.  From your description Szabo's case sounds like a darker shade of grey, though not the darkest. Though it certainly gives a different perspective on movies like Mephisto and Colonel Redl.