Assassinate the convict escaping through the sewers.
Arno approached a fellow Assassin on a rooftop.
- Assassin: Arno.
Look at that. Jean-Baptiste Rotondo escaped prison. Ever hear of him? He knows a few things about the Assassins. It's likely he'll attempt to get to the Templars and tell them what he knows. Assassinate him before the National Guard can reach him. He's right down there, escaping through the sewers.
Arno assassinated Rotondo, denying the Templars information on the Assassins.