Italian law on cybercriminals is the most lax in the developed world, and the Italian legal system is the most worthless in the developed world as well. Hackers actually deliberately move to Italy because they know that they can get away with hacking there. There is absolutely zero chance of Froot being prosecuted in Italy for the 4chan hack.
With that said, he could still easily be prosecuted under Italian law for repeatedly posting "hate speech" on the internet. If there is one thing that European courts actually do focus time and effort on prosecuting, it's wrongthink.