Here are some articles from the local Chicago press from the last time this came up:

http://www.wbez.org/news/chicago-polices-so-called-black-sit...

http://www.chicagotribune.com/news/local/breaking/ct-homan-s...

Not trying to defend CPD here, but the guardian seems to be alone in trying to dramatize this into a story about the Homan Square facility being sort of black ops detention facility.