There is no conclusive evidence. The prevailing opinion of the mainstream is him getting beaten to Death either by Polish, French or Jewish guards in the Detention facility of Althausen.

However that is mostly speculation based on witness testimonies. There are no photographs of him and some other Nazis stated to have seen him in the middle East. A German journalist even claimed to have photographed him as a free man in Germany. Altough the photo was never publicised, the local administration took his claims seriously enough to investigate.

The corpse which is attributed to him is not fully confirmed to be his. While it is the strongest evidence which is public, there are still minor dissonances and some details are still kept secret. His corpse was also under further investigation 2 yeara after it was stated that the corpse belong to him.