This is not made clear in the novel NIGHT, but many people in Europe did not believe such atrocities occurred. This is not due to a lack of proof, but because people were in denial that something so horrific could take place in their backyards and they did nothing to stop it.
In Paris, and in other cities, when the Jews who survived returned to their family homes, they found that others had moved in and felt little sympathy toward the survivors. Comments like, "Hey, we thought you died in the war" were offered as excuses for why they had moved in and claimed all that was left (which wasn't already plundered by the Germans or other thieves).
Many Jews whose families were deportd and killed in the war are still trying to claim family money that was in Swiss bank accounts, paintings, silver, jewelry, and other valuables which were confiscated during the war even today.
Hope this helps you understand...Good Luck! For more information on the subject, you might do a Google search on Holocaust issues.