27 Aug 1941:BroI's scan is taken from HW 16/45. The action in which "Police Battalion 320 shot 4,200 Jews" took place at Kamanets-Podolsk. Below I discuss some facts concerning how the intercepted information in this message first came to light.
Police Regiment South shot 914 Jews
Police Battalion 320 shot 4,200 Jews
In 1996, wartime decodes by the British of German messages concerning shootings of Jews were published and widely reported, such as here and here. The Kamenets-Podolsk decode was summarized in the latter link as follows:
Typical of the messages intercepted by the British is one dated Aug. 27, 1941, from the German commander in Ukraine, Friederich Jeckeln, which records that Order Police Battalion 320 shot 4,200 Jews near the town of Kamenets-Podolsk. Four days later, Jeckeln reported that the same battalion had executed a further 2,200 Jews.This was part of a wider action that was documented in many sources, which Roberto summarized here, and the YVA here, and also in several other decodes that Breitman summarized in Official Secrets pp.62-65. However, a point that requires clarification is whether these publications relied on the original in HW 16/45 or one of the copies held in another folder or at another archive. Breitman takes it from NA RG 457, Box 1386 whereas Hanyok (p.69) cites the "Signals Intelligence Pass[ed] to the Prime Minister, Messages and Correspondence.” HW 1/62, September 1941." Shooting are also listed in Appendix B of Vol XIII of GCCS Air and Military History entitled"The German Police", a copy of which is HW 16/63.
In conclusion, as far as I know, BroI's scan may be the first that has been taken directly from HW 16/45 but its true import is how if fits a chain of evidence consisting of pieces that have been sitting around since 1941 but which only come to light in a piecemeal manner that has to be reconstructed. Most importantly of all, each piece confirms the veracity of the others, and it is particularly significant that British intelligence had no desire for these pieces to come to light.