Ok, this chapter just confirmed the main info we were already given: it's impossible that someone from outside could've done the murder and the murder weapon was definitely a crossbow.
That said, there are new info to take into account now:
1. The place where Ciro's body was found was NOT where the murder took place.
2. The murderer shot Ciro from an estimate distance of 20 to 50 toise(40 to 100 meters).
3. The murder took place at noon, meaning there was no way someone could've infiltrated unseen.
4. The vines on the outer walls are too thin for someone to climb... however I won't discard their use in the murder yet.
5. The first person to find Ciro's body was Monique.
Still, not enough to form a reasonable theory but I have to say I'm thoroughly enjoying this murder mystery.