As it stands arresting people only works in the nexus. As it should right?
But that's only ground floor upwards. If anything this is backwards, if only a certain area, it should be within the prison complex itself.
I've seen a lot of cops wandering around the prison with a prisoner trying to arrest him with no clue as to why they're not being arrested. To rectify this I suggest that the prison complex is either encompassed in the nexus "radius" or it is the only place where a prisoner can be detained.
20 cop cars blocking the road outside of the nexus is a disaster waiting to happen, so their parking in the garage, being able to arrest would ease the parking issue too.