http://www.bbc.co.uk/news/world-us-canada-14564182

The idea was simple – take a group of volunteers, tell half of them they are prisoners, the other half prison wardens, place them in a makeshift jail and watch what happens.

The abusive prison guard, Mr Eshleman, also felt he gained something from the experiment. “I learned that in a particular situation I’m probably capable of doing things I will look back on with some shame later on,” he said.

“It does tell us that human nature is not totally under the control of what we like to think of as free will, but that the majority of us can be seduced into behaving in ways totally atypical of what we believe we are,” he said.