My heart sank when I met him. He stayed at Hartheim for several days that time and often came back. Whenever he was there he addressed us daily at lunch. And here it was again this awful verbal crudity: when he spoke about the necessity of this euthanasia operation, he was not speaking in humane or scientific terms, the way Dr. Werner at T-4 had described it to me. He laughed. He spoke of 'doing away with useless mouths', and that 'sentimental slobber' about such people made him 'puke'. In mid-1941, Wirth was involved in the "euthanasia" program in western areas of Poland; his activity during this time is obscure. In August 1941 Wirth was transferred out of T-4. Operation Reinhard After the T4 "euthanasia" program was halted due to an outcry from the German church, Nazi leadership came up with the "Final Solution to the Jewish Question". The first phase of the "Final Solution" was Operation Reinhard (), headed by Odilo Globocnik. The first out of three Aktion Reinhard extermination camps was Bełżec. Since Wirth had previous experience in murdering with gas in the "involuntary euthanasia" program, Globocnik appointed him as the commandant of Bełżec in December 1941. Belzec became fully operational for gassing on or around 17 March 1942. Before coming to Belzec, Wirth became acquainted with the gas vans in operation in Chełmno and in the eastern occupied territories of the Soviet Union and learned their advantages and disadvantages. This experience in euthanasia, where permanent gas chambers had existed, and with the gas vans inspired his solution. He decided to combine in Belzec the permanent gas chamber with the internal combustion car engine as gas supplier. Wirth objected to the bottles of carbon monoxide gas that had been used in euthanasia institutions. The bottles, which were produced in private factories and which would be supplied to Belzec in large quantities, could arouse suspicion. In addition, the factories were located at great distances from Belzec and the steady supply of the bottles might cause a logistical problem. Wirth preferred to set up a self-contained extermination system, based on an ordinary car engine and easily available gasoline and not dependent on supply by outside factors...Wirth carried out experiments to determine the most efficient method of handling the transports of Jews from the time of their arrival at the camp until their murder and burial. He developed some basic concepts