In October 1939 (I cannot remember the exact date; about the 12th or so), Hitler appointed Himmler to the post of Reichskommissar für die Festigung deutschen Volkstums (= Reich Commissioner for the Consolidation of German Ethnicity).
In that post, Himmler was given two authorisations by Hitler:
1. To undertake all measures to promote the settlement of ethnic Germans in the newly conquered areas; and
2. To undertake all necessary measures against any population group that constituted a danger to the German people.
It is clear that the second authorisation was all that was necessary for Himmler to instruct the SS and police under his command to carry out acts of violence against the Polish ruling class, particularly those elements of it that were hostile to Germany. There was no need for Hitler to issue any further specific orders.
Steve asked:
Here is a passage from the essay by Michael Foedrowitz "Auf der Suche nach einer besatzungspolitischen Konzeption: Der Behehlshaber der Sicherheitspolizei u7nd des SD im Generalgouvernement", in the book edited by Gerhard Paul and Klaus-Michael Mallmann, "Die Gestapo im Zweiten Weiltkrieg: 'Heimatfront' und besetztes Europa" (2000).The theory that the killings took place because of the agreement with Stalin is certainly a radical new interpretation of these events and I look forward eagerly to further elaboration of this.
Page 350:
Note that Foedrowitz backs me up in my assertion that the AB-Aktion was one of the measures undertaken in accordance with the agreement between Germany and the Soviet Union made on 26 September 1939.Ob es zwischen NKWD und Gestapo zu einer konkreten Zusammenarbeit hinsichtlich der Bekämpfung der polnischen Widerstandsbewegung gekommen ist, muß die Forschung erst noch beantworten. Zwar war man vertraglich übereingekommen, keine nationalistischen Regungen der Polen zu dulden und sich gegenseitige Amtshilfe bezüglich eines Informationsaustausches bei der Bekämpfung des Untergrundes zu gewähren, konkrete Vorgänge sind allerdings bis heute nicht bekannt geworden. Dabei scheint sich eine deutsch-russische Absprache bzw. Koordinierung bei der Ermordung der führenden polnischen Klasse im April/Mai 1940 geradezu aufzudrängen: bei den Massenmorden des NKWD in Katyn und bei der AB-Aktion im Generalgouvernement. Es wäre eine seltene Parallelität der Geschichte, wenn die beiden in Intention und Durchführung identischen Maßnahmen dem Zufall entsprungen sein sollten.
My translation:
It remains to be answered by research whether a concrete cooperation between NKVD and Gestapo in regard to the combatting of the Polish resistance movement ever came about. To be sure, they had made a contractual agreeement not to tolerate any nationalist stirring among the Poles, and to provide each other with organisational assistance with regard to an exchange of information in the combatting of the Underground, but concrete actions have not become known even today. Even so, we seem to be positively compelled to accept a German-Russian discussion and/or coordination in the murder of the Polish ruling class in April/May 1940; in the case of the mass murders by the NKVD at Katyn and in the case of the AB-Aktion in the Generalgouvernement. It would be a very rare parallelism of history if the two measures, identical in intention and execution, turned out to have arisen from coincidence.