|Action T4 (German: Aktion T4) was a program, also called Euthanasia Program, in Nazi Germany spanning October 1939 until August 1941, during which physicians killed 70,273 people specified in Hitler's secret memo of September 1, 1939 as suffering patients "judged incurably sick, by critical medical examination", but described in a denunciation of the program by Cardinal Galen as long-term inmates of mental asylums "who may appear incurable".|
The Nuremberg Trials found evidence that German physicians continued the extermination of patients after October 1941 and evidence that about 275,000 people were killed under T4.
The codename T4 was an abbreviation of "Tiergartenstraße 4", the address of a villa in the Berlin borough of Tiergarten which was the headquarters of the General Foundation for Welfare and Institutional Care (Gemeinnützige Stiftung für Heil- und Anstaltspflege). This body operated under the direction of Philipp Bouhler, the head of Hitler's private chancellery, and Dr Karl Brandt, Hitler's personal physician. This villa no longer exists, but a plaque set in the pavement on Tiergartenstraße marks its location.
One of the victims was Hitlers Cousin Aloisia Veith. Hitler's 49-year-old cousin was one of thousands of people with mental disabilities the Nazis killed at Hartheim Castle through lethal injections and gassing.