Karl Brandt and Philipp Bouhler are appointed by Adolf Hitler to lead the T4 Euthanasia Program. The T4 is an abbreviation of "Tiergartenstrasse 4," the address in Berlin where the main offices for the Welfare and Institutional Care (Gemeinnnützige Stiftung für Heil und Anstaltspflege) are located.
The two of them will be responsible for supervising the killing facilities at Hadamar, Schloss Grafeneck, Schloss Hartheim, Sonnenstein, Bernburg, and Brandenburg.
At this time, Professor Karl Brandt is Hitler's escort physician, and Philipp Bouhler is chief of the Private Chancellery of the Führer.
It's not a coincidence that this order comes on the same day as the German invasion of Poland. The elimination of "unworthy" Germans is expected to make room for war casualties; the elimination of "unworthy" Poles is expected to free up resources for Germany.
The order, personally signed by Adolf Hitler, authorizes Brandt and Bouhler to
"broaden the powers of physicians designated by name, who will decide whether those who have — as far as can be humanly determined — incurable illnesses can, after the most careful evaluation, be granted a mercy death."
Hitler's order will actually be written in October, but is back-dated to this date. As many as 90,000 people will be murdered between now and August 1941 on the basis of these orders.