Murder in the city?

Exploration Stage: City Hall
From: Detective
Description: Borgia treasures have been long lost, I have no idea where to look for them. I hope City Hall has some records Help me find any mentions of Borgia treasures, this'll help in the murder investigation.
Completed: You've found records about the Borgia family treasures. Okay, diadem... How interesting! It says here that the diadem does not exist by itself. It appears only if you put together five other Borgia treasures that are called "minor jewelleary". The first of them is Cesare's pin. Wait, I'll tell you its story...