Salieri's confession itself was never anything more than a rumor. Following his delirium and suicide attempt, it was said that he confessed to a priest that he poisoned Mozart, but there is no such written note or testimony (I suppose there couldn't be, since priests don't reveal confessions). Again, we can't prove with mathematical certainty that he didn't confess, but given that he had many mutual friends with Mozart and that they defended him from these accusations throughout this period, we have no reason to believe such a thing.

If you consider Mozart's own letters to be credible historical sources, he wrote about Salieri's attempts to sabotage his career.

There is correspondence between Mozart and his father about a cabal of Italians (especially the court composer Salieri) hindering him. I would say this reflects worse on the Mozarts than it does on Salieri, who spent almost his whole life in Vienna and didn't belong to any Italian cabals. In any case, Mozart established himself rapidly in Vienna and his complaints about Salieri, with whom he had friendly relations, trailed off.

This kind of thing is now a reason to accuse someone of the lowest kind of murder out of jealousy?