Prisoners at Saguaro Correctional Center, which is operated by the private prison firm Corrections Corporation of America, in Eloy, Arizona, October 16, 2009. (Monica Almeida / The New York Times)

The nation's largest private prison firms are still cutting corners despite millions of dollars in federal income tax breaks. Corrections Corporation of America and GEO Group avoided a combined $113 million in federal income taxes in 2015 alone.