Hi. My father in law was also at BAB21, I have extensive research on the camp along with many photos, I am in touch with two surviving inmates, I also have details on the march, which began on the 21st of Jan 1945, they had to return to camp, due to deep snow, they could not get through to the camp at Riegersfeldt, they left again the next day, they were liberated from Moosburg by Patton, 29th April 1945.
If I can help in any way, please let me know.
Regards. K