There needs to be two things.
1, a wandering high level enemy named 'The Kneecapper' who wields a unique bow.
2, a unique bow carried by this guy also named 'The Kneecapper' that slows the opponent on hit. Also it should transform them instantly into a Whiterun guard and send them sprinting there, yelling "I USED TO BE AN ADVENTURER UNTIL I TOOK AN ARROW IN THE KNEE"