He's a tax collector, he keeps his books. When we come looking for his murderer, we don't want them to hold anything over us, like, say, a few hundred Septims that didn't get plundered from his corpse. I am sure the grateful townspeople will reward us manifold for our honesty, although their apathetic responses may not betray their desire for justice.
In lighter news, Yook is looking very swanky in his sky-man clothes. Does he run exceptionally fast with the scroll as well?