Let's also have the truth about the Bologna railway station bombing that same year, in return.
An investigation that ended this year (actually 2020, three years of appeal confirmed the original sentence) concluded that the bombing was organized and funded by a group of people most notably including Licio Gelli, the head of Propaganda Due. Now P2 had contacts with just about everyone, but I think this just makes the question of going further beyond less relevant, since Gelli worked for many people but ultimately only worked for himself.
Of course Francesco Cossiga had his own theory he repeated various times in old age like he did for many events from the Years of Lead (he was the one Amato claims to have gotten this information about the Ustica massacre from - note that he was President of the Council during both): according to him the attack was actually organized by Palestinian terrorists and carried out by different perpetrators. I find that one of his least believable claims however.
