In order to carry out  »Aktion T4«, the T4 had five psychiatric facilities (Grafeneck, Bernburg, Hadamar, Hartheim, Pirna-Sonnenstein) and a former prison (Brandenburg) in the German Reich converted into killing centres. Outwardly, they operated as state hospitals and (nursing) homes. In each killing centre, more than fifty men and women worked as doctors, nurses, clerks, drivers, security guards and »disinfectors«, who burned the bodies.

As of early in the summer of 1940, the T4 set up so-called intermediate institutions in the vicinity of each killing centre, where patients were collected for a few weeks before being murdered. This measure served the purpose of concealment and allowed each murder facility to adapt to the existing »killing capacity« at that time. T4's front organisation carried out the transfers of the patients, using buses of the Reichspost (Reich post office) to do so.

The way the killings took place was largely identical in all six killing centres. Upon arrival, the patients were tricked into believing that they were entering a normal hospital. They had to undress for the supposed initial examination. After their personal details were checked, they were superficially examined by a doctor and photographed by T4 employees. Nursing staff led the patients into the gas chamber that was disguised as a shower room. A doctor operated the gas tap. After they were killed, SS men broke the gold teeth out of the bodies. In order to eliminate the traces of the crime, the dead were cremated.