This is what mobster francesco "frankie the strangler" di Carlo had to say,

"I was not the one who hanged Calvi. One day I may write the full story, but the real killers will never be brought to justice because they are being protected by the Italian state, by members of the P2 masonic lodge. They have massive power. They are made up of a mixture of politicians, bank presidents, the military, top security and so on. This is a case that they continue to open and close again and again but it will never be resolved. The higher you go, the less evidence you will find."

This excerpt is referring to the murder of God's banker Roberto Calvin who fled to london after losing the Vatican vast sums of money

It was the mafia who carried out the dirty deed, on behalf of the P2 lodge

I'll add that the fact Calvi was found hanged under Blackfriars bridge speaks volume. It is known that masons commonly refer to each other's as "friar" therefore to be hanged under Blackfriars bridge bears significance seeing Calvi lost their money

They had him on a boat and could have got rid of his body in multiple ways ie throw him in the river Thames..that would have been the much easier option. Plus it would still be considered suicide. Or make him do the Houdini (dismemberment)

The killers had to carry dead weight up scaffolding and hang him under the bridge which was no easy task. They were sending a message