Originally Posted by dswallow
Prisoners would grab keys off guards that wandered close... except perhaps prisons where the doors didn't have locks and were only controlled remotely, or otherwise where such locks simply were in a location not reachable from inside a cell.
I know this thread is dead, but since it's infected, we have to kill it again - aim for the head this time.
Anyway, most modern prisons have remotely controlled cell doors that a) require power to operate and b) have a manual override to open the cell doors if there is no power, or they fail open - meaning that if power fails, the cells automatically open.
Prisons don't have power backup that lasts for 6 months, so I would assume that after some time in the cells, once the power ran out, the cell doors just opened and they were free to roam the cell block and get killed.