Vill Dester is the only merchant whose shipments are getting through the kobolds without incident, and our agent caught him pouring something into the Lantern Hook well. We need more information before we can accuse him of colluding with the kobolds, however.
So, Karkh saw a liquid drip into the well, and it smelled like oranges? Vill Dester sells fruits and vegetables. Karkh's testimony, along with Anontok's notes, is all the evidence I need. All that's left is to confront Dester.