Speak to Elling Trias in Stormwind.
That Marzon would be contacting a member of the Defias and have ties to Lescovar...
Having killed VanCleef and Thredd, it would be hard to see Lescovar brought to proper justice, as your evidence is nothing without their testimonies. That is not even considering the fact that Lescovar is a noble and well connected. It effectively makes him above the law.
You'll need other help. I loathe to do so, but there is someone I know that will aid us. You'll find Trias in the Trade District of the city.