The cruelty of crimes committed by the Nazis during World War II is beyond belief. Ethnic cleansing focused mainly on the Jewish community and has been spoken of the loudest since the end of the war, but this was not the only course of eugenic thought. People who had been harmed by birth – the disabled and mentally ill, were not spared the torturers wearing German uniforms. This article presents the circumstances involved relating to the activities of AktionT4 in Germany and the territories under German occupation, and performs a legal analysis of these activities in the light of international law in the so-called Doctors’ Trial, the first of the follow-up processes to The Nuremburgh Trial. The author introduces the legal bases of the sentences issued in the trial and highlights the process of shaping the responsibility of individuals in international law. The participation of Polish law enforcement agencies in prosecuting crimes against humanity committed on the patients of psychiatric hospitals and care centers in Poland, is also addressed. The proceedings in this case have been ongoing to this day, now conducted under the auspices of the Institute of National Remembrance.