Flamestrike
Legend
I am curious - do these high level NPCs has nothing better to do than chase after low level murderers?
They're either NPC adventurers (getting paid) or agents of the powers that be (Bane Clerics, Assassins, Zhent warriors etc for the Zhents, Assassins and so forth for the Thieves Guild, or Champions, War Clerics, Mages, Knights and so forth for the local Lord).
I mean the Lord of Beregost (a town of 3000 people) is 16th level. He's not only the lord (so with access to Guard NPCs and a few Veterans etc) but also a big deal in the church, and can contact the Flaming Fist mercenaries (who are responsible for policing adventurers) in Baldurs Gate if he cant handle the PC's personally.