Although concentration camps in the Independent State of Croatia were established as early as April and May 1941, acts of legal force first mention them on June 26, 1941 in the Extraordinary Legislation and Order of Ustasha Chief Ante Pavelić. Only the Legal Provision on Sending Unwanted and Dangerous Persons to Forced Stay in Concentration and Labor Camps should have introduced more order and systematicity. According to that provision, only political prisoners could be sent to concentration camps on the basis of written decisions of the competent police or judicial authorities. The period of forced residence is determined from a minimum of half a year to a maximum of three years. This provision was dealt with in individual cases, and there were significantly more detainees delivered outside the prescribed procedures and without written penalties. They were delivered in mass transports, especially Serbs, Jews and Roma, from the whole territory of the Independent State of Croatia, possibly with some accompanying census, and often without it.
Detainees were most often transported by train in wagons intended for cattle.
"Out of forty freight wagons of the composition, four cattle wagons are full of people. The transport has been on the road for more than seventy hours. One station chief maneuvered the train, another station chief held the wagons on an unknown order, a third chief waited for the new cargo to be attached, and the Ustasha transport commander allowed the train to travel only at night. During the day the train stood on the open track. The September sun warmed the iron sheets of the wagon roofs. The people in the carriages were moaning, reaching through the bars and begging the Ustasha guards to moisten them with water. The Ustashas spat in their palms. People were suffocating in closed carriages. The air entered your lungs as if you were sucking the dry warmed cotton.
Five hundred Ustashas were lined up along the embankment of the railway, outside the Jasenovac railway station; beneath the heavy weapons something barely human peeks out: a face. Ustasha guards open the wagons, and people fall from the wagons and roll down the embankment. The living and the dead. "
Vladimir Carin, Death Walked on Four Legs, Zagreb, Mladost, 1961, 31-32. p.