This is a German movie with English subtitles distributed in 2001.
"The movie is based on the infamous "Stanford Prison Experiment" conducted in 1971. A makeshift prison is set up in a research lab, complete with cells, bars and surveillance cameras. For two weeks 20 male participants are hired to play prisoners and guards. The 'prisoners' are locked up and have to follow seemingly mild rules, and the 'guards' are told simply to retain order without using physical violence. Everybody is free to quit at any time, thereby forfeiting payment. In the beginning the mood between both groups is insecure and rather emphatic. But soon quarrels arise and the wardens employ ever more drastic sanctions to confirm their authority."
The experiment reminded me of the Stanley Millgram experiements done in the early 60s where subjects gave electric shocks to "students" under the supervision of "researchers" to understand the role of punishment in learning. The subjects gave increasingly large dosages of shock when coerced by the "researchers" because of their perception of the "authority" of the "researcher". This study is very reminiscent of the Germans who participated in the holocaust because they were "under orders".
This movie demonstrates the dynamics that ensue when some people are assigned as guards and other people are assigned the role of prisoner. It strikes me somewhat as an adult version of the Lord Of The Flies.
It is quite disturbing to see the lengths that people will go to in order to be in control and to be "right". In an adversarial situation this can escalate up to and including death. The will for dominance/freedom may be more of determining factor in human relations than our will for harmony, cooperation, and peaceful coexistance.
This movie is not "out there" science fiction. It is very believable and seems realistic. If you are interested in human nature, I highly recommend it.