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.