The Prussian Feldjägerkorps was an SA police organization set up as the permanent successor of the former SA Feldpolizei. It was a quite small and noteworthly elite formation within the SA and in practice regarded as part of the Prussian police. Its commander, Walter Fritsch was an SA-Oberführer. The wording "SA Oberst" most probably means SA-Standartenführer. In that case we are talking about two very high-ranking officers of small elite corps, apparently even commanding officers of their respective Feldjägerbereitschaften executed in the purge.Lambeardus Ostendorp (Born 20 May 1893, SA Oberst Feldjagerei. Executed in Dresden 1 July 1934)
Heinrich Nixdorf (Born 19 October 1890, SA Oberst Feldjagerei. Executed in Breslau 30 June 1934)
Who were they and why indeed did they end up on the list? Were they affiliates of the Röhm circle or was it more a personal vendetta? What makes this more peculiar is the fact FJK itself was heavily involved in the purge proceedings, at least in Berlin if not elsewhere in Prussia as well, carrying out arrests and cordoning off areas.
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They were executed in Dresden and Breslau. The purge operations in Breslau and in the whole of Silesia were personally directed by the commander of Oberabschnitt Südost, SS-Gruf. Udo von Woyrsch together with Ernst Müller. Various sources maintain that he had trouble with some of his men. It is also mentioned that there was a major roundup and arrest on an "armed SA camp" which briefly resisted the SS attackers. This might be a focal point, perhaps the SA-Staf. Nixdorf was one of those in that camp.
In Dresden, the Oberabschnittsführer Karl v. Eberstein was responsible but I haven't come across any similar accounts to that of Silesia from there. It is also worth a notice that Ostendorp was executed on the second day of purge. That might imply that he was not one of the main targets but rather belonged to the "second wave" of executions.