There is a saying now here in my country that "No viral no justice" which is given to the police of how bad this institution is in my country. While I also believe that they are needed at times, and should be available as they are being paid by the money from the tax payer, the fact is that this is not always the case.
I believe that there are several factor that gives them the bad image, and mostly it is because of the overall citizen behaviors and culture, the corruption, and also the mentality of the whole country.
Why I say that the citizens played a part is that because they see being a police as a safe job for retirement, and they will do everything so that their kids could get into the police force and the sad thing, is that most of the time they use connection and also money for bribing so that they can send their kids to the police force. also we tend to love breaking the law, especially the traffic, and once we got caught we tend to bribe the police so that we won't get cited for the offense.
since the demand is so high, this is being used by some of the greedy high-ranking people in the force, they try to sell the slot for those who are desperate to be police. and then the bribery can happen.
Next is the politician, who usually has a close connection to the General will usually use its power to save themselves and also their family in case they have some problem with the law. also they will use the police force to secure it business, some of them might be illegal, but with the back-up from high-rank police officers and the politicians to keep them up and running, and exploit all the resources in the country.
But still now, when there is an interesting criminal case, often time the police seems to work fairly only when the case went viral. Thus the saying come "No Viral no justice"