On Asylum (ArmA 3) our police system works as following:
We have a Chief of Police, who is head of the police force as a whole, and head of the Captains.
Secondly, we have the Captains.
Captains are also the leaders of the police force, but will still have to put their decisions and thoughts down by the CoP.
Lieutenants.
Lieutenants are responsible for interviewing people that want to join the police force and are responsible for them completing their exams correctly before whitelisting them.
Sergeants.
Sergeants are mostly an in-game support officer. A Sergeant is responsible for certain callouts that officers of lower ranks are not allowed to make. Also are they responsible for scouting officers that are eligible for promotion. Besides that, they are responsible for doing peoples ride-alongs. Ride-along is needed for when a cadet-week has finished and this officer feels like he is ready for promotion.
Corporals.
Corporals are mainly officers with a bit more in-game abilities. They are also responsible for keeping everything serious and official while on patrol.
Constables.
Constables are normal police officers. They have all basic abilities a police officer needs to perform normal duty. They are also responsible for teaching cadets the ropes and making sure they understand everything before doing their ride-along.
Cadets.
Cadets are newly whitelisted civilians that got accepted in to the police force. They are forced to play cop only for 1 week. They may have their ride-along on the 8th day.
I personally like this system a lot, and I hope something like this is taken in mind when organizing the police force.