In 1971 at Stanford University a psychology experiment was undertaken with university students and locals with 18 psychologically stable men. Paying $15 a day, for what was supposed to last two weeks, nine were made guards and nine made prisoners and did the experiment in a make shift prison in the basement of the psycholgy department building. The got so out of hand that it didn't last a week.
you can read/see the specifics in a slideshow with text at http://www.prisonexp.org done by the developer of the study.
amazingly within 36 hours, regular normal people here, there was already prisoner abuse and sexually tinged humiliation. there were riots, violence, psychological tactics, attempted prison breaks...
there is something about the structure of prison that makes this sort of thing more likely to happen which the report goes into.
this does not mean for a moment that what has happened isn't completely unacceptable and that it could have been prevented et al
but this site gives shocking insight into prison psychology without having to read michel foucault.