Of course, the killings by the German Nazi state happened. There are literally tons of primary sources for the millions murdered by the Nazi government including the 6 million Jews murdered in the Holocaust. The first mass Nazi killings were of ordinary German citizens who were mentally or physically handicapped. The operation was called AktionT4. The victims were approx 250,000 persons the first victim being a little baby his name, Gerhard Kretschmar
The first known victim of Aktion T4 was one Gerhard Herbert Kretschmar who was just five months. When he was murdered – most likely with an injection of a lethal dose of phenobarbital. He was buried in the Lutheran churchyard three days later.
Gerhard was born with disabilities so severe (blind, with either just one leg and with one arm). He was also subject to violent convulsions and was determined to be mentally retarded. Hence his murder fit the definition of a "mercy killing" to a ‘T’.
His parents were Richard Kretschmar, a farm laborer, and his wife Lina Kretschmar, a homemaker. They resided in in Pomssen, a village south-east of Leipzig and had no desire to witness their child’s sufferings.
So they took the newborn Gerhard to Dr. Werner Catel, a pediatrician at the University Children’s Clinic in Leipzig, and asked that his son be "put to sleep."
However, refused Catel telling them that this would be illegal (which it obviously was). And added that the only person in Germany that could authorize the euthanasia, was Adolf Hitler.
So they petitioned their Führer directly to end the suffering of their poor child. More specifically, Richard Kretschmar asked his Führer to overrule the law that protected "This Monster" and other children like him from "mercy killing" thus indefinitely prolonging his or her sufferings and those of his parents and relatives.
As was usual with such petitions, it was referred to Hitler’s private secretariat, headed by Philipp Bouhler (who later became a CEO of Aktion T4). There it was seen by Hans Hefelman, head of Department IIb (and subsequently one of top managers of Aktion T4), which dealt with petitions. Hefelman and Bouhler showed the petition to Hitler, aware of his frequently expressed support for the "mercy killing" of people with severe disabilities.
However, Adolf Hitler did not order the euthanasia right then and there but instead decided to follow “due process” (sort of). Hitler summoned Dr. Karl Brandt, one of his personal physicians, and sent him to Leipzig to investigate the Kretschmar case.
He told Brandt that if Gerhard Kretschmar’s condition was indeed as described in Richard Kretschmar’s petition, then he, Hitler, authorized Brandt to have Gerhard euthanized, in consultation with the local doctors, and if any legal action were taken, it would be thrown out of court.
In Leipzig, Brandt examined the child and consulted with Catel and another physician, Dr. Helmut Kohl (no relationship to famous West German Chancellor). He also went to Pomssen and personally interviewed the Kretschmars. When Brandt informed the Leipzig doctors of Hitler’s instructions, they agreed that Gerhard Kretschmar should be euthanized, as they believed (as most did at the time) that Hitler’s word was above any written law.
This "mercy killing" marked the beginning of Aktion T4 – which ultimately resulted in the deliberate killing of about 200,000 people with mental and/or physical disabilities in Greater Germany and about 100,000 more in German-occupied European countries.