Dubbed The Beast of Belsen by camp inmates, he was a German Nazi war criminal, directly responsible for the deaths of thousands of people.

[3] As commandant at Natzweiler-Struthof, Kramer personally carried out the gassings of 80 Jewish men and women,[4][5] part of a group of 87 selected at Auschwitz to become anatomical specimens in a proposed Jewish skull collection to be housed at the Anatomy Institute at the Reich University of Strasbourg under the direction of August Hirt.

The deaths of 86 of these inmates were, in the words of Hirt, "induced" in an improvised gassing facility at Natzweiler-Struthof, and their corpses, 57 men and 29 women, were sent to Strasbourg.

There were a number of witnesses who said that he took an active part in the selection parades in that, for instance, he loaded people into the trucks and beat them when they resisted.

One of the defendants at the Frankfurt Auschwitz Trial, Dr. Franz Lucas, testified that he tried to avoid assignments given to him by Kramer by pleading stomach and intestinal disorders.

When Lucas saw that his name had been added to the list of selecting physicians for a large group of inmates transferred from Hungary, he objected strenuously.

[9] With the collapse of administration and many guards fleeing to escape retribution, roll calls were stopped, and the inmates were left to their own devices.

During the trial Anita Lasker testified that Kramer had taken part in selections for the gas chamber at Auschwitz.

[11] Kramer was sentenced to death on 17 November 1945, for crimes both at Auschwitz and at Bergen-Belsen, and was hanged at Hamelin Prison by Albert Pierrepoint on 13 December 1945, aged 39.