Under the Galactic Republic, Sector Rangers were assigned to a specific sector of space, and tasked with pursuing criminals deemed too dangerous for local law enforcement. Operating alone or in small crews, they were legally allowed to deputize willing locals. The elite of the Rangers, called Special Enforcement Officers (SEO), enjoyed the jurisdictional freedom of crossing sector borders in pursuit of their targets. Those officers often worked alongside members of the Jedi Order to bring the most dangerous criminals to court.
The Sector Rangers were one of the oldest law enforcement institutions in the Galactic Republic. By the time of the Separatist Crisis, they were a branch of the Republic Office of Criminal Investigations (ROCI), which itself was a division of the Republic's Judicial Department. 
- Star Wars: Scum and Villainy: Case Files on the Galaxy's Most Notorious (First mentioned)
- Rise of the Separatists
- "Crime and Punishment" – Star Wars Insider 209