Q. When we are in doubt as to whether a Jew has sinned, it is meritorious or obligatory to judge him favorably.
I assume by inference, that if this doubt occurs with a gentile, we are not likewise obligated.

In the Kinnah by Moreinu HaRav Shimon Schwab zt”l concerning the Holocaust, there is a phrase therein about the tragedy that the Nazis turned Jewish bodies into soap.

An official in Yad Vashem informed me that they have a department that is involved in researching claims by survivors about atrocities committed in the Holocaust. They say that they have researched this claim and found that there is no evidence that the Nazis ever turned Jewish bodies into soap, and the soap found with the label RJF that was thought to be an abbreviation for Reine Judische Fett did not contain any fat, human or otherwise.
They say that they investigate these rumours and declare those that they find without evidence as unsubstantiated so as not to allow the Holocaust deniers any fuel to suggest that just as these unsubstantiated rumors are fact less, so too is the rest of Holocaust history.

On the other hand, evidence was presented at the Nuremberg trials that German reserchers had developed a process for the production of soap from human bodies. Additionally, it has been quoted in several books the admission by Col. Rudolph Hoess yimach shemo, the Commdandant of Auschwitz, that human fat was collected from the crematoria to produce soap (although I have not yet located this exact transcript).

Considering this doubt, are we permitted to assume that the Nazis did make soap from our Jewish brethren, and that this justifies our mournful cry on Tisha B’Av?

A. Although a quick search on the articles on-line seems to mostly agree that human-fat soap was not mass produced by the Nazis, it seems that it was experimented on and done in small quantities.
Horav Shlomo Miller’s Shlit’a opinion is that in general, not seeing something does not prove it does not exist, (“Lo roinu eino ra’aya” – Edyios 2: 2, Kesubos 23, Zevachim 103b). There is definitely no reason to be “melamed zechus” on most evil individuals, however the truth should always be told when it is evident. In this particular case, as mentioned, it remains on the eyes of the beholder.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a