[1] It is now infamous as the largest of 12 companies that designed and built crematorium ovens for concentration and extermination camps during the Holocaust, planned and carried out by the Nazi regime from 1935 to 1945.

[2] Topf & Söhne's main competitor in making concentration camp ovens was the Berlin firm H. Kori GmbH [de], founded in 1887.

Topf & Söhne was producing heating, brewing and malting systems and working collaboratively with other firms to sell products all over Germany and beyond.

[4] The company began manufacturing incinerators for burning municipal waste and, from 1914, crematoria for local authorities, due to the increasing acceptability of cremation as a means of body disposal.

After graduating from Hannover, he spent a further five years at Leipzig, Berlin, and Rostock universities, studying a wide range of subjects, including economics, law, and sociology.

In the early 1930s, due to the economic crisis of the Weimar Republic, the company lost business to such an extent that by Spring 1933 it was in danger of bankruptcy.

The unusually high numbers looked suspicious, so the SS wanted their own on-site facilities, although it was illegal for crematoria to be outside of local authority control.

As with all Topf & Söhne stationary ovens, the parts were made in the factory in Erfurt, and the firm's staff went on site to build them, often spending months at the camps.

It is also thought that they supplied transportable ovens to at least one of the Nazi euthanasia institutions, in which a total of over 70,000 physically and mentally disabled people were murdered in 1940 and 1941.

In October 1941, the SS placed an order for five three-muffle ovens for the new Auschwitz-Birkenau extermination camp (Auschwitz II), where it was initially estimated that over 1000 people per day would die.

[1] In December 1939, a patent application was made for Prüfer's double-muffle transportable cremation unit, although it was not approved, possibly because of the legal problem of ash mixing.

[1] On 26 October 1942, the engineer Fritz Sander, Prüfer's manager, applied for a patent for what he called a "continuous operation corpse incineration oven for mass use".

[13][14] In early 1943, the Topf & Söhne fitter Heinrich Messing installed exhaust fans in the Auschwitz II crematoria and also in the gas chambers.

[12] Topf & Söhne engineers and other staff visited the concentration camps many times, not only to install and repair equipment, but also to observe processes to help make them more efficient.

[12][14] On 13 March 1943 the engineer Karl Schultze and Heinrich Messing witnessed a test sample of 1,492 Jews from Kraków Ghetto being killed in the gas chambers at Auschwitz II and then cremated.

Abuse is known to have occurred; the camp manager, Wilhelm Buchröder, a Nazi, was dismissed in 1944 by Ernst Topf for beating Zwangsarbeiter, although it is reported that his successor also mistreated them.

However, in an administration office at Birkenau camp, the Soviets found documentation relating to Topf & Söhne, detailing "the construction of the technology of mass death, complete with the precise costs of crematoria and calculations of the number of corpses each could incinerate in a day".

[14] The US Army's Counter Intelligence Corps (CIC) started to investigate Topf & Söhne within a few days of the Buchenwald liberation, and took company documents.

[20] On 27 April 1945, Ludwig Topf organised a meeting with company's works council at which it was agreed that the line to be taken with investigators was that workers and management knew that the ovens were delivered to concentration camps, but that they did not know the details of what was going on.

He maintained that the ovens they had delivered to the concentration camps were standard equipment, of the same type that they made for city crematoria for civilian use and claimed that if they had refused to work with the SS they would have been severely punished.

[1] Later, in December 1946, because of his membership of the Nazi party, the Fritzlar-Homberg Spruchkammer, a German civilian denazification court, started investigating Ernst Topf.

This closed at the end of 1949 and Topf's file was handed over to the Wiesbaden state prosecutors office, where investigations into him as an accessory to murder for his role in the Holocaust began.

[4][23] Fritz Sander, Prüfer's manager, who was 70, died of heart failure on 26 March 1946 in Berlin, three weeks after his arrest and after four interrogation sessions.

In 1994 Sabine Leutheusser-Schnarrenberger, the German Justice Minister, also refused that claim because, she said, the factory was used to manufacture the "murder machinery of the extermination camp.

[26][27] Squatters moved onto part of the site of the former factory on 12 April 2001 and set up an independent culture centre known as Das Besetzte Haus (the occupied house).

They ran social and cultural projects, and organised events and guided tours which drew attention to the history of Topf & Söhne during the Nazi period, which had been largely forgotten.

[26] The factory workshops no longer remain, but a museum and education centre opened in the former administration building on 27 January 2011, Holocaust Memorial Day.

[5] The motto "Stets gern für Sie beschäftigt, ..." ("Always happy to be at your service, ...") is painted in large letters on the outside of the restored building.

This bland valediction (complimentary close) was often used at the end of letters Topf & Söhne sent to the SS, in which details of orders for concentration camp ovens were discussed.

[30] In 2007 the Dutch broadcaster VPRO made a television documentary about Topf & Söhne called The Big Denial as part of the In Europe series.