most conspiracy theories are a bit true if you dig enough, it's just that some of the crazy ones weave the threads together in very twisted ways, usually in support of some deep seated collective fears
and yes, it was an america conspiracy against the rise of communism in europe post ww2, all europe was under us control (still now somehow), italy particularly so because of our commie inclinations. we were a threat. cold war, ye?
after 50 years the reponsibles have not been found, they are protected by the highest powers. all the dynamics of the kidnap + killing are not proven and inconsistent and so even the alleged testimonies of the people who declared to have commited the crimes... only lately the politicians started to reveal the role of some unspeakable puppeteers... it's very crazy stuff, you won't find it on wikipoodia.
(side note, and that was not the only case...)