Can this "libretto" prove Salieri killed Mozart?

No. It can't. That's ridiculous. Yet Jess Staufenberg of The Independent wants us to think it can.

Antonio Salieri is now best known for something he didn't do: killing Wolfgang Amadeus Mozart. The 1984 movie Amadeus is most responsible for the persistence of this myth into the twenty-first century (and it is a fantastic movie!), but the idea predates the Oscar-winning film by over 150 years. The movie is an adaptation of a Tony Award-winning play from 1979 by Peter Shaffer, which itself was based on Alexander Pushkin's play Mozart and Salieri from 1830, which was based on rumors that circulated after Mozart's death that were proven false.

The story resonates with viewers because it touches on one of our most powerful emotions, jealousy. We all know a Mozart--someone who is just better than you at something without even trying. No matter how diligently you work, someone will always be able to beat you, and it's particularly infuriating if they mock your efforts in the process. It's a common human experience projected onto famous historical figures, which is often a recipe for successful entertainment. It's historically false, but it's really good fan fiction.

So, when a Czech museum finds a collaborative composition by Mozart and Salieri that has been lost for two centuries, the Amadeus angle is the obvious route to generate page views. Frankly, if you don't at least mention the rivalry, your reader will be distracted by the thought, "Wait, didn't Salieri kill Mozart or something?" It'd be irresponsible not to mention it.