The Guard (1990)

Most stories about prison brutality are set among the prisoners. This unusual feature follows the initiation period of a new guard who has come onto a train taking prisoners to forced labor camps (gulags). Each day, the train travels farther from "civilization", and each day, the brutal treatment the guards mete out to the prisoners and the rough games they play on each other grow in ferocity and barbarity. The new guard somehow bears the progressive dehumanization of himself and his fellow guards, until something happens and he loses all control.