Wikipedia
The "Kugel-Erlass" (bullet decree) also known as "Aktion Kugel" was a secret decree (Geheimbefehl), issued by Nazi Germany on March 2, 1944. The decree stated that escaped Allied prisoners of war, especially officers and senior non-commissioned officers, should be handed over to the Sicherheitsdienst who should execute them, "im Rahmen der Aktion Kugel", in concentration camp Mauthausen.
This order was in direct contravention of the provisions of the Third Geneva Convention.
An exception was made for escaped British and American POW's. Their fate was to be decided by the German High Command (Oberkommando der Wehrmacht) on a case-by-case basis.
The Bullet Decree was soon amended to include British soldiers after the "Great Escape" of 25 March 1944.
The number of escaped POW's executed by the Kugel-erlass is not precisely known. Estimates vary between 1,300 and 5,040 executed POW's. The vast majority of these POWs came from the USSR. Five escaped Dutch officers are known, and four more are suspected, to have been executed in Mauthausen as a result of the Kugel-Erlass.