In the spring of 1941, the SS leadership and the »Chancellery of the Führer« decided to murder concentration camp inmates who were unfit to work. The murder campaign carried the designation »special treatment 14f13«. It was directed by Viktor Brack, who had already organised the T4 killings. As of August 1941, responsibility for the killings was transferred to the SS Economic and Administrative Main Office.

The selections began in April 1941, first in Sachsenhausen and then in other concentration camps. Modelled on the murder of patients, selection was carried out on the basis of registration forms, pre-selection by the camp commandant, and the medical »assessment« by T4 staff that had travelled there, such as Friedrich Mennecke. The victims, among them Olga Benario-Prestes, Mary Pünjer or Jerzy Kahane, were murdered in the gas chambers of still existing T4 killing centres (Bernburg, Pirna-Sonnenstein and Hartheim). Victims of »Aktion 14f13« were, in particular, prisoners who were unfit to work, but also those who were Jewish, politically undesirable or deemed to be »asocial«. The increasing demand for workers from among the camp inmates led to an almost complete halt of the murders up to the spring of 1943.

The second phase of the »euthanasia« of concentration camp started in April 1944. After a simplified selection process, it was the weakened prisoners from the concentration camps of Mauthausen and Gusen in particular who were murdered by gas in Hartheim. The number of victims can no longer be precisely determined. It is estimated that 15–20,000 people died in the first phase of »Aktion 14f13«.