Sadly, for many centuries and in actual days, police can do something that is not supposed to be done, but since the majority don't know their rights, they will do whatever goes into their minds, as a entertainment. But if you work for some department of Justice, they ignore to serve Justice, since they assume that anyone that works for the Justice System, can do anything they wish, like they do, when someone doesn't know their rights.
These days, Police freedom is a bit more controlled, but since they are not monitored for every single step or action they can do, the abuse continue. For example, in some countries police cannot open the doors of your car. They need to ask you to open the doors, but if you look like someone that is not from that specific country, they will open, explore anything that is inside your car and since you know nothing about the Law, you cannot block their activity. This is a good reason to read about the laws of any country you going to visit. It will prevent some Police abuse. For example in Marrocos, you can have big problems with police, but if you don't mind to give an extra money (police corruption), they give you the freedom you need, while sometimes you didn't anything wrong, but they don't like you (for some non-sense reason) and you can have big troubles with them.