I feel like your fake identity is a good call with the flaying. It is a lot of effort to go to for no other apparent reason. Even as a warning the dragonborn was ditched in water and may never have even come ashore so poor way to make a display. The only other thought I had would be some sort of spell components or ritual components but why would you need all the scales.
With the insight park killing I wonder if we are reading too much into it? Maybe the victim was thrown into the hedge and stabbed with the ritual dagger and the magic bit is just related to the ritual dagger? This would make the cause of death more consistent (strength based anchor, bashed, hung) with one use of breath weapon. This then fits with a strong dragonborn sorcerer using disguise self to slip in and out and relying mostly on the physical prowess for the murders.
Torn between harbormaster and graveyard at this stage
