Dubbed political prisoners by Nazi Germans, in reality, many of them including school teachers, lawyers, and priests were caught at the Nazi-Soviet demarcation line trying to cross the border to get to France through Hungary. According to Tarnów historian Aleksandra Pietrzykowa, on the evening before the transport, the 728 Polish prisoners were rounded up based on a previously prepared list, and ordered to take a shower and to disinfect themselves in a public bath. They were then detained until the early hours of 14 June, when the whole group, escorted by the SS, were marched out of the prison and along the deserted Tarnów streets to the railway station. There, all were pushed into the waiting rail cars.