We found some information about Moritz Moshe Heller in the Memorial Book for the German Jews
In September 1944 he was transported from Westerbork to Theresienstadt and shortly after to Auschwitz. Many prisoners were transported from Auschwitz to Bergen-Belsen at the end of 1944 and the beginning of 1945 and he probably was among them. The 1st March 1945 was the official date he was declared dead.
In a liberation list of Theresienstadt there is an entry for his wife, born 2nd July 1920. We assume that she was deported together with her husband to Theresienstadt but she stayed there while Moshe was transported to Auschwitz. Indeed his wife survived and came back to Holland.