27% of prisoners are illegal immigrants
[...] At the federal level, the number of criminal aliens incarcerated increased from about 42,000 at the end of calendar year 2001 to about 49,000 at the end of calendar year 2004--a 15 percent increase. The percentage of all federal prisoners who are criminal aliens has remained the same over the last 3 years--about 27 percent. The majority of criminal aliens incarcerated at the end of calendar year 2004 were identified as citizens of Mexico. We estimate the federal cost of incarcerating criminal aliens--Bureau of Prisons (BOP)'s cost to incarcerate criminals and reimbursements to state and local governments under SCAAP--totaled approximately $5.8 billion for calendar years 2001 through 2004."