Incarceration 101 - http://www.incarceration101.com/prison-gang-activity.php

How Gangs Took Over Prisons - http://www.theatlantic.com/magazine/archive/2014/10/how-gangs-took-over-prisons/379330/

Pirate Economics 101 - http://freakonomics.com/2009/04/20/pirate-economics-101-a-qa-with-invisible-hook-author-peter-leeson/

Why Prisoners Join Gangs - http://www.economist.com/blogs/economist-explains/2014/11/economist-explains-7

Podcast - Social Order of the Underworld - http://www.econtalk.org/archives/2015/03/david_skarbek_o.html