What happened to Keller in the camp? What happened to Keller’s finger?

Henisch tells Paul that after Keller returned home, he sewed a yellow star to his clothing and registered as a Jew. He was then sent to the Auschwitz concentration camp in 1942. Henisch also tells Paul that Keller was part of the prisoners, who were forced to march from Auschwitz to Buchenwald to Bergen-Belsen, and that he died on the last journey. Paul asks how he knows this, and Henisch shows Paul his own six-digit tattoo.

Hesistantly, Paul tells Henisch about Keller's new life, that he didn't die, and that Keller was, in fact, his own piano teacher in Australia. Henisch doesn't believe it and tells Paul that he, himself, saw Keller fall.

Paul then tells Henisch that Keller has a finger missing from the right hand, to which, Henisch responds that Keller had all his fingers. Henlisch acknowledges, however, that an SS guard once asked Keller to play the piano in the camp, and after Keller refused the guard told him that if he ever felt the desire to play again he would cut off his fingers one at a time.