According to a recent report by the Bureau of Justice Statistics, there were only 7,444 official allegations of sexual abuse by guards in detention in 2008, and of those, only 931 were substantiated. These are absurdly low figures. But perhaps more shocking is that even when authorities confirmed that corrections staff had sexually abused inmates in their care, only 42 percent of those officers had their cases referred to prosecution; only 23 percent were arrested, and only 3 percent charged, indicted, or convicted. Fifteen percent were actually allowed to keep their jobs.

http://www.nybooks.com/articles/archives/2011/mar/24/prison-rape-and-government/