In order to make the investigation more realistic, Zimbardo arranged with a police department to have the 'prisoners' arrested.
Day 3
Guards wore khaki guard uniform and were given sunglasses, a whistle, baton and handcuffs. The prisoners wore a short smock top with their number on it, as well as a chain around their ankles, and no underwear. The initial behaviour of the participants was unrealistic and they used to laugh.
Day 5
Keep scrubbing, you idiot! It needs to be spotless!
One of the guards became known as "John Wayne", as he was more brutal and aggressive than the rest, like the roles of John Wayne.
Day 6 & the end
After the guards became more brutal, and banned the prisoners from leaving their cells, one prisoner showed extreme signs of anxiety, but wasn't allowed to leave until day 4.
I CAN'T TAKE IT ANYMORE!
The guards made the prisoners clean the toilets with their bare hands. At night the guards sexually humiliated the prisoners.
The power of the guards was almost total and prisoners obeyed without question. Visiting postgraduate Christina Maslach objected strongly and convinced the researchers to stop the study. Zimbardo concluded that the reason for the behaviour of both the guards and the prisoners was to conform to their social roles, not their personality.