What's Pashto for F***!!!!!?
Seems there were Afghan guards and NATO forces on duty. They didn't notice anyone missing for hours. Let me repeat that: they didn't notice that nearly five hundred prisoners were suddenly gone, for hours. At least some of the prisoners were confirmed "bad guys," including Taliban.
The escape was conducted through a tunnel that took months to produce, laid out to weave around any defenses and lead to waiting vehicles.