While you were out, I asked around.
You are looking for Overseer Durant. Turns out he lives near the Shimmershade Garden.
I can help you confront him, but you will need help. There are three individuals with the necessary skills, and they serve our cause.
Tell Cyrille that the owl hoots at dusk.
Inform Lorin that the saber prowls the plaza.
Mention to Sylessa that the cruel caskmaster has breathed his last.
They will know what to do.
Speak to Vanthir when the deed is done.