The Sutthoff database says Alexander van Gelder died there 6 Dec 1944
https://www.ushmm.org/online/hsv/person_view.php?PersonId=8255928
Date of Birth: 27 Aug 1903
Place of Birth: Harlingen
Last Residence: Amsterdam
Date of Death: 6 Dec 1944
Prisoner Number: 99508
Prisoner Group: HOL. JUD.
Source: International Tracing Service (ITS)