Id like to see a some changes done to the police ranks.
Level 1 Recruit
Level 2 Officer
Level 3 Corporal
Level 4 Sergeant
Level 5 Lieutenant
Detectives are a specialized part of the rank system.
Also on the rank insignia on the sleeves can be held the same. Although for the Lieutenant rank instead of keeping it the same as a Sergeant it can be a Silver Bar.
And also for the Chief it should be ranked as Captain.
This will greatly help distinguishing high ranked and experienced officers.