How does Zalman, the boy running with Elie, die in chapter 6 of Night?

During the winter of 1945, not long before the work camp at Buna is liberated by the Russians, Wiesel and his father are evacuated. The evacuation is basically a forced death march from Poland to the German concentration camp at Buchenwald, where Wiesel's father dies and Wiesel himself is ultimately freed.

Wiesel, who was only 15 at the time, has a badly infected foot and is barely able to keep up as the SS guards drive the men relentlessly through the snow with threatening words such as "swine" and "filthy sons of bitches." Any man who could not keep up the pace was shot by the guards. For a time a young man named Zalman marches beside Wiesel until he is overcome with stomach cramps and needs badly to relieve himself. Despite Wiesel's pleas for Zalman to keep going, the boy eventually stops and pulls down his pants to purge the waste that has caused his spasms. Wiesel reports that it was the last time he ever saw Zalman. He believes the boy was probably trampled to death rather than being shot by the SS.