Ustica is an excellent example of how in Italy there are two versions of recent history, each one apparently well documented and between themselves fundamentally irreconcilable.
Well, Ustica actually has a lot more than two versions. I remember when the court determined that it was a MiG going supersonic in close proximity to the jet.
So you've got USN drop tanks in the debris field, a Libyan MiG-23 in the mountains of Calabria, an Italian air force with a high mortality rate to those exposed, including car accidents, suicides and the Ramstein Airshow, Ghaddafi's flight plan through the region (although he flew a different route), and the French showing up on NATO radar recordings (which a court saw fifteen years ago, but never made public, to my knowledge). Add in bombings in Bologna, and you've got enough missiles, shockwaves, bombs and coverups to explain every major transit disaster in Italy clear through to the Costa Concordia.
No one theory is ever going to fit all the "facts". They never do, especially when an event generates "facts" with such regularity as this one. Conspiracy theorists also have a handy epistemology: if it supports their case, it's a known fact; if it goes against their case, it's evidence of a cover-up.
Bomb in the toilet? Probably.