On any given day, three-quarters of a million people are jail inmates and two-thirds of them haven't been convicted of anything, according to US Department of Justice statistics. They are awaiting trial, and an estimated 80 percent of them cannot afford to pay bail.

Most won't go to prison: Overall, 95 percent of those booked into local jails in 2010-11 were not subsequently sent to prison, says Timothy Murray of the Pretrial Justice Institute (PJI). And 75 percent of felony defendants will be judged innocent, given probation, or sent to rehabilitation programs and never end up being sentenced to prison, says longtime correctional researcher James Austin.