Dr. Stefan Szende, a Swedish-based Jew of Hungarian origin, described the alleged mass extermination at the Belzec camp as follows:
"The death factory comprises an area approximately seven kilometres in diameter. (...) The trains filled with Jews entered the underground rooms of the execution factory. (...) The naked Jews were brought into gigantic halls. Several thousand people at one time could be filled into these halls. The floor was of metal and was submergible. The floors of these halls, with their thousands of Jews, sank into a water basin which lay beneath - but only far enough so that the people on the metal plate were not entirely under water. When all the Jews on the metal plate were in the water to over their hips, electrical current was sent through the water. After a few moments, all the Jews, thousands at once, were dead. Then the metal plate was raised out of the water. On it lay the corpses of the murdered victims. Another shock of electrical current was sent through, and the metal plate became a crematory oven, white hot, until all the bodies were burnt to ashes. (...) Each individual train brought three to five thousand, sometimes more, Jews. There were days on which the lines to Belzec supplied twenty or more trains. Modern technology triumphed in the Nazi system. The problem of how to exterminate millions of people was solved."
(Stefan Szende, Der letzte Jude aus Polen, Europa Verlag, Zurich-New York 1945, p. 290 ff.).
At Belzec the Jews were killed according to eyewitness Jan Karski as follows:
"The floors of the car had been covered with a thick, white powder. It was quicklime. Quicklime is simply unslaked lime or calcium oxide that has been dehydrated. Anyone who has seen cement being mixed knows what occurs when water is poured on lim. The mixture bubbles and steams as the powder combines with the water, generating a large amount of heat. Here the lime served a double purpose in the Nazi economy of brutality. The moist flesh coming in contact with the lime is rapidly dehydrated and burned. The occupants of the cars would be literally burned to death before long, the flesh eaten from their bones. Thus, the Jews would "die in agony"", fulfilling the promise Himmler had issued "in accord with the will of the Fuehrer", in Warsaw, in 1942.
Secondly, the lime would prevent decomposing bodies from spreading disease. It was efficient and inexpensive - a prefectly chosen agent for their purposes. It took three hours to fill up the entire train by repetitions of this procedure. It was twilight when the forty six (I counted them) cars were packed. From one end to the other, the train, with its quivering cargo of flesh, seemed to throb, vibrate, rock, and jump as if bewitched. There would be a strangely uniform momentary lull and then, again, the train would begin to moan and sob, wail, and how. Inside the camp a few score dead bodies remained and a few in the final throes of death. German policemen walked around at leisure with smoking guns, pumping bullets into anything that by single motion betrayed an excess of vitality. Soon, not a single one was left alive. In the now quiet camp the only sounds were the inhuman screams that were echoes from the moving train. Then these, too, ceased. All that was now left was the stench of excrement and rotting straw and a queer, sickening, acidulous odour which, I thought, may have come from the quantities of blood that had been let, and with which the ground was stained.
As I listened to the dwindling outcries from the train, I thought of the destination toward which it was speeding. My informants had minutes described the entire journey. The train would travel about eighty miles and finally come to a halt in an empty, barren field. Then nothing at all would happen. The train would stand stock-still, patiently waiting until death had penetrated into every corner of its interior. This would take from two to four days."
- Jan Karski, Story of a Secret State, The Riverside Press
This Jan Karski was, by the way, appointed to chair a committee for "Scientific Research on the Holocaust". Really, he was.