The mortuary book was kept by Stanisław Ryszler (no. 16439), a kapo of Leichenträger kommando. Leichentrager kommando was responsible for taking corpses of dead prisoners or prisoners killed in the camp hospital, prisoners shot against the Death Wall, prisoners hanged at the assembly square or prisoners who died in residual blocks to the mortuary located in the basement of Block 28.
The mortuary book witnessed the numbers of almost 23,000 dead prisoners, whose corpses were collected in the mortuary before they were cremated. Before any assembly, records of the mortuary book were compared with records of the death book kept by the office of the hospital.
The mortuary book is a small notebook in hard cover. A recorder made columns in which he wrote: prison number of a dead prisoner, date of transfer of a corpse to the mortuary, and place (number of a block or kommando) where a prisoner died or were killed.
Source: http://www.auschwitz.org/en/museum/about-the-available-data/death-records/leichenhalle/
(The above text is briefly copied from the above mentioned website.)