In the National Socialist conception of race, the Roma and Sinti (derogatively called: “Gypsies”) had a special paradoxical status. Although Roma and Sinti had come from India and were thus considered more “Aryan” than even the Nordic races, they had inbred with “lesser races” and were thought to have sacrificed their purity. As a result, these "mixed-breeds" [Mischlinge] were considered racially predisposed toward asocial tendencies and were regarded as “degenerate criminals and vagabonds” who posed a threat to the security and the health of the German people. Himmler in particular was fascinated by the "Gypsy question." In 1936, he founded the Racial Hygiene Research Center within the Reich Bureau for Health in Berlin for research and the gathering of statistics on the approximately 30,000 Gypsies living in Germany. The information collected by Dr. Robert Ritter was later used for the systematic persecution, forced sterilization, and murder of "Gypsies." Estimates of the total number of Roma and Sinti killed during the Nazi genocide range from 220,000 to 500,000. After the war, Dr. Ritter continued to practice in the area of psychiatry. Criminal proceedings against him were closed in 1950.