During the Holocaust, Tesch sold vast quantities of Zyklon B, utilizing his pesticide as a way to commit genocide.

Tesch then took over the management of the Berlin branch of the German Society for Pest Control (Degesch) GmbH.

[3] The patent was assigned to Degesch, "Deutsche Gesellschaft für Schädlingsbekämpfung mbH" (German Limited Company for Pest Control), subsidiary of I.G.

Farben, with Walter Heerdt being the only one of the inventors to receive patent rights, a portion of the proceeds from the manufacture and sale.

It was primarily a pest control company specializing in fumigation of commercial properties such as the warehouses and freighters in the Port of Hamburg.

[citation needed] In 1925, Tesch & Stabenow—partly due to the largesse of Paul Haber of Degesch—received the exclusive rights to distribute the insecticide Zyklon B east of the Elbe River.

[4] During World War II Tesch & Stabenow sold massive quantities of Zyklon B to the SS.

The gas was sent to Auschwitz, Sachsenhausen, Neuengamme, Gross-Rosen, Majdanek, and Ravensbrück concentration camps.

Allegedly, when Tesch was asked for his views, he had proposed to use the same method, involving the release of prussic acid gas in an enclosed space, as was to exterminate vermin.

He was fired for unknown reasons after the firm building suffered an air raid in July 1943.

He said he never attended a conference discussing the subject, had not devised any methods for using Zyklon B other than fumigating the barracks, and had not known that the gas was being used to kill people.

At the same time, Freud was facing pressure from high command to release Tesch, since British occupation forces were using Zyklon B to fumigate their ships.

He and Pelican told high command that Tesch's case was the first time they were dealing "not with people directly concerned in the murder or ill-treatment of prisoners or slave workers, but with those who lent their skill and services to facilitating the gruesome work of the concentration camps and so identified themselves with breaches of the laws of war on a wholesale scale.

Freud and Pelican started digging through other files, and found that the firm had a sharp rise in profits in 1942 and 1943, when the mass gassings were at their peak.

However, they could not find anything suggesting that Tesch, or his employees, knew their product was being used to kill people instead of vermin.

[5] During further questioning, Freud reported that Tesch adopted an attitude of ignorance carried "to an absurdity."

Freud reported that Weinbacher was "blindly obedient, has a slow brain", and was "an arrogant man with limited intellect."

Freud and Pelican, becoming desperate, organized a meeting with hidden microphones, hoping that Tesch might incriminate himself.

Bahr, a medical officer, had earlier been identified by a survivor of Neuengamme concentration camp as having participated in the murders of hundreds of prisoners.

In May 1946, a British military court found him guilty of war crimes and sentenced him to death for actively participating in mass murder.

Bahr insisted to a horrified Pelican that the victims were killed "painlessly and humanely", and had all died within minutes.

However, on one occasion, he had been ordered to empty tins of Zyklon B into a sealed barracks filled with approximately 200 Soviet POWs.

The prosecutor was British Army Major Gerald Draper, who argued that Tesch knew the SS was using Zyklon B to systemically exterminate human beings, and had chosen to continue selling massive quantities of the gas to them.

The prosecutor presented several other witnesses who backed the existence of the report: Karl Ruehmling, who had been a bookkeeper and assistant gassing master for the firm, said that Zyklon B was sent by Tesch to Auschwitz, Sachsenhausen, and Neuengamme.

Draper said Tesch's actions and knowledge made him an accomplice to murder, and that Weinbacher was just as guilty.

He said that Tesch and Weinbacher appeared to know everything about their business, but were sensitive to talk about the Zyklon B sales to Auschwitz.

The Judge Advocate said Draper was asking, "Why is it that these competent business men are so sensitive about these particular deliveries?

However he then asked the judges what were the odds that, throughout the entire war, Weinbacher had only paid attention to the figures related to other dealings, and never to those concerning the Zyklon B sales.

He concluded that regardless of how much Drosihn knew, he could not legally be found guilty without having been in a position to influence the sales.