To kill their victims, Aktion T4 murderers used almost exactly the same methods as did the perpetrators of the Holocaust. Which was no surprise as the former subsequently selected and implemented the tools and technologies employed in the latter.
There was a minor difference, however – children were euthanized by injection of poisonous chemicals, typically phenol; the cause of death was usually listed as “pneumonia”.
The choice of this method was financial – it was found that extermination of smaller groups was more economical by injection of each victim with phenol. It was subsequently used to kill inmates of concentration camp sentenced to death by then SS. The most famous victim was Maximillian Kolbe – a Polish Franciscan friar who volunteered to die in place of a stranger in Auschwitz.
Like the Jews in the beginning of the Holocaust, thousands of T4 victims were shot by the SS men of the Einsatzgruppen. More specifically, by Einsatzgruppe VI under the command of Herbert Lange (subsequently the Commandant of the of the Chełmno extermination camp).
Soon it was recognized (as would happen two years later during the Holocaust), that shooting was an inconvenient method of mass murder. So the T4 murderers graduated to using the poison gas; however, they used pure carbon monoxide, not Zyklon-B.
The first experiments with the gassing of patients were conducted in October 1939 at infamous Fort VII in Posen (now the Polish city of Posnan), where hundreds of prisoners were killed in an improvised stationary gas chamber developed by Dr. Albert Widmann, chief chemist of the German Criminal Police (Kripo).
Two years later (when the T4 program was ostensibly officially terminated), another poison was tested – the exhaust fumes of car engines. In the mental hospital in Mogilev (now in Belarus) a room with twenty to thirty of patients was closed hermetically, and two pipes were driven into the wall thus creating a makeshift stationary gas chamber.
Two cars were parked outside, and the metal pipes connected the exhaust tubes of the cars to the pipes in the wall. The car engine was turned on and the carbon monoxide began seeping into the room. In a few minutes later all those in the room were dead.
To maximize the flexibility and adaptability of T4 operations, it was predictable decided to use mobile gas chambers – gas vans. Curiously enough, these killing machines were invented not in Nazi Germany, but in the Soviet Union – in 1936, -in the beginning of Stalin’s Great Purge (Great Terror).
And the inventor of this diabolical apparatus was not German or even Russian – he was a Jew. Namely, Isay Berg, the head of the administrative and economic department of the Moscow regional office of NKVD (Soviet Secret Police – a rough equivalent of Nazi RSHA). Quite predictably, two years later Berg himself became a victim of the Great Purge.
The gas vans were specifically designed to direct deadly exhaust fumes via metal pipes into the airtight cargo compartments, where the intended victims had been forcibly stuffed to capacity. In most cases the victims were suffocated and poisoned from carbon monoxide and other toxins in the exhaust as the vans were transporting them to fresh pits or ravines for mass burial.
Although the T4 killers began using gas vans almost four years later – in 1940 for the gassing of East Prussian and Pomeranian mental patients in the Soldau concentration camp, there is no evidence that its inventors knew about its Soviet predecessors.