That's my problem with them. If they had been killing Soviets in ranking positions, it's understandable, but killing Polish citizens could never be acceptable in such circumstances, even if they were turncoats.
There was no peace treaty with the soviets nor any legitimate polish government during the occupation , Poland was at war until 1989
Pawian, correct me if I'm wrong, but I think Poland was never formally at war with the USSR, hence there could be no peace treaty.
As for the Polish government, the one in charge then was recognised as the Polish government by the international community. There's a reason why the III RP takes its legal continuity from the PRL and not from the II RP.