What happened to Peter Van Daan after he was captured by the Green Police?
On August 4, 1944, Peter and the others were taken from the annex and held overnight for interrogation at the police headquarters. From there, they were transferred to a prison located about one mile south of the annex. Within a week, they were deported to Westerbork transit camp in the Netherlands. On September 3, having arrived at Auschwitz-Birkenau, the group was separated by gender on the platform. Peter was assigned a relatively safe job, reportedly in the mail room, and survived the camp. Ten days before the Red Army liberated Auschwitz on January 27, 1945, the SS evacuated the remaining prisoners on foot, leaving only a few thousand of the sickest behind. Otto Frank was among the ill in the infirmary, and he tried to convince Peter to stay and hide. Confident of his relatively good health, Peter chose to leave.
There are no certainties about what happened to him beyond the gates, but it is believed that Peter made it to Mauthausen, in Austria, where a prisoner with his name was registered on January 25, 1945 and assigned to mining labor. In April, records show that he was taken to the infirmary, where he died in early May, around one week before Mauthausen was liberated by American soldiers.
Peter was with Anne in Westerbork, and the two were often seen together. Once they got to Auschwitz, however, they were separated. When the Auschwitz prison guards fled the camp to avoid the oncoming Allies, they took most of the prisoners with them. Peter went with the group of prisoners led by the guards through the bitter winter weather. Many died along the way—of cold, hunger, or gunshot—and Peter was among them.
Sorry, but The Diary of Anne Frank states that Peter is taken with the SS as they try to escape from the Russian's, who are on the move. It states that Peter is never heard from again after that. I presume he is , sadly, dead by now. If you do not believe me go look in the "Afterword " of Anne's Diary.