It seems like the impetus to follow one lead to its conclusion ended with the weaponsmith.
I voted for Sorcerous Sundries, mostly on the off-chance someone there might recognize a ritual being done through the murders. Though without knowing if anything was taken from the corpse at Insight Park that might be premature.
I thought the Harbormaster's Office, might give us another sighting of Fel, possibly when the Dragonborn first came to his attention. But if all the murders are taking place near Riverveins, then that doesn't totally follow.
