Complex sentence: Another is that De Mauro had discovered drug trafficking between Sicily and the United States, and a third with the Golpe Borghese a planned right-wing coup d'état (the plan failed in December 1970).
Split into simpler sentences: Another is that De Mauro had discovered drug trafficking between Sicily and the United States. A third explanation links his disappearance with the Golpe Borghese a planned right-wing coup d'état (the plan failed in December 1970).