The Prison Key Card is an item in Shadow Man. It is found in the Gardelle County Jail and allows Shadow Man to open all gates in this level and connect all three (formerly separate) areas.
It is found by going through Batrachians schism, in one of the outside courtyards.
Find the receptacle on the wall with the two red lights on it, press the action button to slide the card, it will show two green lights then the gates will open somewhere in the level. The key was still being gripped by a permanently dead headless inmate, when it is used the arm is still attached.
Key when first found