Of all of those writing about Roma, the neurologist Dr. Robert Ritter was to play the decisive role in terms of supplying "scientific" justification for the coming genocide. Under his leadership, the "Research Centre for Genetic Sciences" was founded by the Interior Ministry in 1936; from 1937 it was known as the "Research Centre for Racial Hygiene and Population Biology", located at the Ministry of Health in Berlin-Dahlem. In 1935 Ritter had already publicly attacked Roma at the International Congress for Population Studies in Berlin: he cited his "Studies into genetic experiments within a reproductive circle of gypsy half-castes and asocial psychopaths" and demanded the forced sterilisation of members of this social group.

As early as this work Ritter had presented the "interbreeding of Gypsies and the native-born" as the cause of asocial and criminal behaviour. this insane idea was repeatedly "scientifically reappraised" and modified anew by the "Research Centre" and it was elevated to a key position in Nazi racial theory on Roma.

Ritter complained that everyone who was suspected of being Roma "denied it": he saw the task of his institute to compile an "inventory of Germany's entire Gypsy population". The "discovery and documentation of half-castes" was a prerequisite for "solving the Gypsy question". Ritter and his staff (E. Justin, R. Ehrhardt and K. Maravek) published a stream of works outlining "solutions", all of which had a decisive impact on legislation against Roma. Kenrick and Puxon see Ritter's 1937 article "A Breed of People" as a death sentence for the Yenish - Ritter casts them as the descendants of vanquished tribes and thus not Aryan. This article was supported by, among others, ministries' police representatives and various church bodies in Freiburg and Rottenburg.

In order to make the institute's work easier, Himmler orders that the head office of the "Gypsy Centre" be moved from Munich's police H.Q. (possessing by then some 19,000 files on individuals and families) to the state Investigative Police Department in Berlin. The Munich office now became the "Reich Centre for the Combat of Gypsy Disorder". A decree by the SS on December 16th 1938, again to facilitate Ritter's inventory work, ordered that "all persons without fixed abode, as are Gypsies, are to report to the police and be inspected for the purposes of racial biology". A second injunction of December 17th 1939 forbade them to leave their then place of residence. Ritter's institute then sent teams of workers trained in "genealogy" and "racial biology" to all parts of Germany to document Roma. Unwilling subjects were threatened with sterilisation or deportation to the camps. Ritter's best-known staff member, Eva Justin, was also active for the Gestapo; Ritter himself had even visited several concentration camps where Roma were detained. This work was supported financially by the German Research Community among others.

Collecting all of this information eventually led Ritter to locate approximately 28,000 Roma and Sinti in Germany (eventually including Austria and the Sudetenland) between 1938 and 1942. By the latter date, 19,000 had had been "racially evaluated". Merely 1,079 were of "pure race", of "wholly Gypsy descent", as were 500 Lalleri; the remaining 90% were classified as "half-castes". 1,800 were classified as non-German Roma with "certain features in common with Jews", while those in Austria's Burgenland were described as also being clearly "a population of half-castes".

Ritter's aim was to identify so-called "quarter and one-eighth Gypsies". Most of these did not even know that one of their great- grandparents had been Roma, and who, in the case of Sinti, were often fully integrated with the German population, some even serving in the army. Ritter described the "part-Gypsies" as "carriers of less valuable genetic material", as "extremely unstable, without character, unpredictable, untrustworthy, difficult, flighty...". Ritter's depiction of the supposed danger they posed was to be the death sentence for thousands. It is here assumed that quarter and one-eighth Gypsies" were taken to the camps while "quarter and one-eighth Jews" generally remained unharmed.