According to Moshe Gross, the deportations began on October 26, 1940, when Grabowski arrived in the ghetto and held a number of conversations with the Jewish representatives. He and two Gestapo officers informed Hahn and Landau that the patients selected by them for transfer to convalescent homes would be taken away. The patients had to be washed and dressed in fresh underwear.
The gas vans were provided by Sonderkommando Lange. SS-Sturmbannführer Herbert Lange from the Gestapo in Posen was previously tasked with the extermination of the mentally ill in the Wartheland and on Greiser’s order experimented with gas vans as a new form of mass killing from early 1940. Lange acted under the direction of SS-Standartenführer Ernst Damzog and the Higher SS and Police Leader, Obergruppenführer Wilhelm Koppe.
The Warthegau euthanasia program was part of a larger euthanasia program, born out of the Nazi conclusion that the mentally and terminally ill patients are "a social ballast" and should be "killed out of mercy" (German: Gnadentod). It targeted Jews and non-Jews. Lange started the Warthegau action in October 1939 by liquidating an asylum in the vicinity of Posen with about 1,000 patients who were deported to the city of Posen and gassed at Fort VII. Lange then abandoned the use of this fortress and started to build gas chambers on the chassis of trucks. Throughout the rest of 1939 and 1940, he proceeded to murder the patients of the state psychiatric institution "Dziekanka" in Gniezno (Gnesen), the hospital in Kościan (Kosten), the mental hospital "Kochanówka" near Łódź (Litzmanstadt), and the psychiatric hospital in Warta, before moving to Kalisz....