Perhaps it was manipulated ...but the fact is that the behaviour described based on a rapport de force does exist.

[dailymail.co.uk]

Famed Stanford prison-experiment shows naturally abuse power based LIES！！！

It was recently outed in the first half of this year, that the whole Stanford Prison experiment was a fraud, Zimbardo had skewed the results to get what he wanted by secretly briefing some of the participants before hand, instructing "guards" to be tough and having a drama student fake a mental breakdown.
This talk is ten years old, when the reputation of the experiment was still in tact.

I'll have to look at this later when I go to bed. His prison experiment was pretty bloody evil. I prefer to think people have changed since his experiment but it would be unethical to replicate it.