&gt; Are there any eyewitness accounts written online, in any language?

I am not sure if this is really any help to you, but I recall reading a story about a Jewish boy that lived in Belarus in WW II, in "Время секонд хэнд" (Vremya sekond khend, Second-hand Time) by Svetlana Alexievich. The boy crawled from a massive pile of corpses, his family nowhere to be found, before joining the partisans in the war. However, I am not sure if this is the same execution as the one you are mentioning. Furthermore, I must stress that Alexievich herself says she is not a journalist and that the apparent witnesses in her books are fiction.
包含语种1:English，语种2:Russian