The deadline was nearly a decade ago yet Homeland Security still can’t track when visitors to the U.S. leave the country — leaving deportation officers struggling to try to find millions of people who have managed to disappear into the shadows, according to a new watchdog report Thursday.

Officers have to use 27 different computer systems to try to figure out someone actually left the country when they were supposed to, presenting a gargantuan task that often stymies their efforts to spot and kick out illegal immigrants, the Homeland Security inspector general reported.

And the data the officers are using is so bad that they often get false negatives, meaning a target appears to have left the country even though they never did — allowing criminals to remain at large in the U.S. without anyone looking for them.