In Blackshirts and Reds, Parenti also talks about how East German officials who prosecuted collaborators were, after reuinfication, held liable to West German laws that made their earlier rulings illegal.
From the footnote on page 83:

Helene Heymann, who had been imprisoned during the Hitler regime for her anti-Nazi activities, later was a judge in the GDR, where she presided over anti-sabotage trials. She was put on trial in 1996. When her conviction was read out, it was pointed out by the judge that an additional factor against her was that she was trained by a Jewish lawyer who had been a defense attorney for the Communists and Social Democrats.