Betrayal was rife during WW2, it was a time where you couldn't trust anyone anymore. There's multiple stories about that in Maus, where people betray their own people and family to gain favors with the Nazis (there's some essays about that if you can't be bothered to read the graphic novel, e.g. here https://brandeis.digication.com/rkoehler/conflict ).

That is, the Nazis gave a Judas some food and other favors if they could find and report jews in hiding.