You must provide some evidence, be it circumstantial, before the investigation is started. And that is why you cannot do like in Robespierre-an France and just wave your finger pointing at everyone.

People in many regions of Italy are used to quakes, like people living in California. In such regions is normal to be aware that something might happen, and that is why during these episodes people are trained to sleep outside, in their car, if they feel uneasy. Here the authorities have been telling the people: don't worry, nothing is gonna happen. That's not how you behave, especially when you perfectly know that the are is at high seismic risk.

You are right, and that is why those guys are being prosecuted: they tried to calm the population claiming that there would be no big quake, that everything was absolutely secure, and that those who claimed the contrary (actually there was one person) were just fools.

Ok, maybe you need to know something about the Italian judiciary system. In Italy there is something called "obligatory penal action", which means that if there is even the simple suspect of a crime being committed, then an investigation must be started.

In the quake case, the investigation started because the people responsible for monitoring the situation explicitly reassured the population by telling them that there would be no big quake. Any responsible scientist, given the continuous small shakes that were ongoing, would have at least said something on the line "We believe there will be no major quake, but please do not lower your guard".

And that is why there was an investigation that ended with them being charged for negligence.