Which year did the Nazis start to kill physically and mentally disabled people?

Explanation

Nazi Germany started executing physically and mentally disabled people in 1939 and managed to kill some 70,000 altogether during World War II. In 1942 the systematic killing of Jews commenced. Before that, it had mainly been persecution and the erection of ghettos. The original idea was to ship the imprisoned Jews to Madagascar, but instead, some 3 million Jews were killed inside concentration camps in the years to come, alongside an unaccounted number outside the camps.