At Mauthausen, on the other hand, functionary positions remained dominated by criminal prisoners until just before liberation. The system and hierarchy also inhibited solidarity among the prisoners. There were tensions between the various nationalities as well as between the various prisoner groups, who were distinguished by different Nazi concentration camp badges. Jews wore yellow stars, other prisoners wore colored triangles pointed downward. Prisoner functionaries were often hated by other prisoners as Nazi henchmen and were spat upon. While some barrack leaders ("Blockälteste") tried to assist the prisoners under their command by secretly helping them get extra food or easier jobs, others were more concerned with their own survival and, to that end, did more to assist the SS. Identified by green triangles, the "Berufsverbrecher" or "BV" ("career criminals") kapos, were called "professional criminals" by other prisoners and were known for their brutality and lack of scruples. Indeed, they were selected by the SS because of those qualities. According to former prisoners, the criminal functionaries were more apt to be helpful to the SS than political functionaries, who were more apt to be helpful to other prisoners. From Oliver Lustig's "Dictionary of the Camp": The SS used domination and terror to control the camps' large populations with just a few SS functionaries. The system of prisoner guards was a "key instrument of domination", and was commonly called "prisoner self-government" ("Häftlings-Selbstverwaltung") in SS parlance. The camp draconian rules, constant threat of beatings, humiliation, punishment, and the practice of punishing whole groups for the actions of one prisoner were psychological and physical torments on top of the starvation, and physical exhaustion from back-breaking labor. Prisoner guards were used to push other inmates to work harder, saving the need for paid SS supervision. Many "kapos" felt caught in the middle, being both victims and perpetrators. Though "kapos" generally had a bad reputation, many suffered guilt about their actions, both at the time and after the war, as revealed in a book about Jewish kapos. Many prisoner functionaries, primarily from the ranks of the "greens" or criminal prisoners, could be quite ruthless in order to justify their privileges, especially when an SS man was around. They also played an active role in the beatings, even killing fellow prisoners. One non-criminal functionary was , a notorious Austrian political prisoner.