Inquisitor Vilhelm's Sinstone

Inquisitor Vilhelm has taken exceptional precautions to protect his sinstone. Broken into several pieces and hidden from sight, he believed his sinstone would be safe from us. But his plan had the same weakness as most: he trusted weak-willed underlings. I "interrogated" several dredgers to learn where they helped the inquisitor hide the broken fragments of his sinstone. Find all the fragments and bring them to me.