If he could slip in undetected then the inmates could slip out undetected. Barbed wire was meant for cattle, not humans. Concertina wire is meant for humans. Guessing, just like with Epstein, the guards were sleeping.
If the prisoners are totally accounted for, in the building and in their cells, is it unreasonable to relax the perimeter security? It can beefed up again when the prisoners are out in the yard. This is a county jail, not a supermax prison. At the best of times, the security here is not going to state-of-the-art because the typical profile of the prisoners here do not warrant that high a security level. This incident is more of an embarrassment to the local jailers than the sign of a serious security problem.
If this jail routinely housed seriously dangerous, violent criminals, do you really think that officials would have placed it within a stone's throw of a high school?