[This](https://en.wikipedia.org/wiki/Gleiwitz_incident) Much of the testimony regarding it came from the nuremburg trials, which are automatically suspect in my view. The official story is that the Germans staged false flag attacks against German border posts/towns and left behind a few bodies in Polish uniforms to cement the impression that attacks were carried out by Poles. Allegedly the bodies were poor innocent jews who had been killed by lethal injection. Now the part about jews being slaughtered I'm fairly sure is the usual holohoax fantasising, but the incidents themselves did happen because the Germans made a point of publicising them before the war. I doubt the Poles were the actual perpetrators given that they had everything to lose from provoking a war, and the Germans refused access to the sites of the attacks by international observers, so it seems likely the NSDAP cooked them up to create pretext for the invasion.