Nit-picking here, but I am not sure this person is accused of genocide. This person is not wanted in relation to the genocide of the Jews in WW2, but for his participation in the retaliation killing of Polish civilians. Today I learned that Germany killed about 5 million Polish, mostly civilians, during WW2 [1], which is mind-boggling. But I don't know if this was ever classified as genocide, as this was not done with the intent of exterminating the Polish population in part of whole (which is the definition of genocide [2]), while the Jews were killed with precisely that intent.
[1] https://en.wikipedia.org/wiki/Collective_punishment#By_Germa...
[2] https://en.wikipedia.org/wiki/Genocide_Convention