In this study, Zimbardo chose 21 participants from a group of 75, all male students, previously screened for mental illness and paid $15 per day . He then assigned roles. One being a prisoner and the other a prison guard, there were 3 guards per 8-hour shift, and 9 prisoners in total. Shortly after the prisoners were arrested at their homes, they were taken to the local police station, registered, processed, given appropriate prison attire and given identification numbers. Before the study, Zimbardo had concocted a prison setting in the basement of a Stanford building. It was as authentic as possible with the barred doors and plain white walls. The guards were also provided with proper guard attire, without weapons. Shortly after beginning the experiment, with the guards and prisoners naturally beginning to assume their roles, Zimbardo planned for the experiment to last about a fortnight. Within 36 hours, one prisoner had to be released due to erratic behavior. This may come from the sadistic character that the guards adopted quite quickly, dehumanizing the prisoners through verbal, physical and mental violence. The prisoners also took on their own roles quite effectively. They started to denounce the other prisoners and said