What were the clues that help told that the Nazis were lying?

Inquiries were made about family members. THe Jews were told that family members had been relocated-- but later when they're taken to the station themselves they see the baggage of their family members.

When arrive at the train they see their bags and belongings spread out over the train tracks. The soldiers then order them all to lay down, but when they're not quick enough a bullet is shot at the ground near their feet. Afterwards, they are crammed into the boxcars and locked inside.