What is the main conflict in Death and Judgment by Donna Leon?

The book starts with an accident taking place near the city of Travisio. A truck from Romania derails and the driver and several women are killed. The entire incident is a mystery as is the presence of the women.

Prominent attorney Carlo Trevisan is murdered on the intercity train to Trieste. There seems to be no obvious motive, but the case is assigned to Brunetti. Not long after the murder of Trevisan, Rino Favero, a prominent accountant in Padua is also murdered. Although the two murders have no obvious links, Brunetti has a gut feeling that they are connected. When Trevisan's phone number is found in Favero's notebook, Brunetti's feelings are confirmed.