Every year 10 million people funnel in and out of U.S. jails and prisons, and some get lost, NPR reports. Evan Ebel walked out of a Colorado prison four years too early; two months later, he allegedly rang the doorbell of Tom Clements, the head of the Colorado Department of Corrections, shot him in the chest and killed him. Stephen Slevin, pulled over for driving under the influence in New Mexico, was left in solitary confinement for almost two years, never brought before a judge and never saw a lawyer. He won a $15 million settlement. “I’d be very surprised if there is a county jail anywhere in America that hasn’t released a pre-trial prisoner early or held one longer,” says Art Wallenstein, who heads the Montgomery County, Md., corrections department. “You could have simply a wrong number placed on a release document. You could have an X drawn through a case by mistake. You could have a detainer that just came in as someone was being released. I’ve been doing this for a terribly long time and it hasn’t got any easier.” “For the most part, sentence calculations are being done by hand,” says Michela Bowman of the National Council on Crime and Delinquency. The criminal justice system depends on court clerks to record judges’ orders correctly, prison and jail administrators to read instructions properly, and staff to accurately add and subtract good-time credits.