mistreatment of prisoners is not exactly rare on this planet. just last week there was a case uncovered here in Germany, where groups of prison guards with masked had regulary massaged prisoners with batons over years, leading to severe injuries and broken bones.

http://de.news.yahoo.com/040506/336/40o17.html
the link only has the story in german, sorry, but it does not appear to have been very newsworthy.