In The Boy in The Striped Pajamas by John Boyne, what did Shmuel's father do?

In
chapter 12, Shmuel describes his former life before he was taken to Auschwitz and separated from
his family. From the other side of the fence, Shmuel tells Bruno that he used to live with his
parents and brother above his father's watch shop. Shmuel's father collected, repaired, and sold
watches for a living. Shmuel goes on tell Bruno that his father once gave him a beautiful watch
with a gold face before the Nazi soldiers took it away from him. Shmuel then elaborates on how
the Nazi troops invaded his community and began issuing edicts which separated and oppressed
Shmuel's family and the rest of the Jewish population before they were transported to
concentration camps. Toward the end of the novel, Shmuel's father disappears, and he petitions
Bruno for help finding him. Tragically, Shmuel is not aware that his father has been executed in
the gas chambers along with the other Jewish prisoners and desperately searches the camp with
Bruno before they are also herded into a gas chamber.