A lot of the SS were not directly involved with what happened to the Jews. They may have not even have been at Melmedy as was believed.
There is a quote from a man who was in the SS who knew what was going on but was repulsed by it. He stated years later, “There were those who did not know what was going on, and I do not know there fate. There were those who knew what was going on and didn’t think it wrong, and I suspect I know their fate. Lastly, there are those of us who knew what was going on, knew it was wrong, and did nothing to stop it, and I suspect I know our fate.”
It was entirely possible to be SS and not have been in the purification units.