Prior to uniformed police, law enforcement was a largely private matter, and private "thief-takers" were enlisted to apprehend criminals. My understanding is modern state-run police forces developed in response to public anger over misconduct and corruption in the thief-takers, such as the Macdaniel affair.

Particularly they were infamous for playing "both sides" by taking money from a victim to arrest a thief, then taking money from the thief not to arrest them.