OOC: Yes, the POD for this DBWI is simple, Antonio Salieri really poison Mozart, and Mozart actually buried in clear, marked, non excavated grave, enough for 20th century investigators to gain the sample of his remains and finally confirm the murder. Salieri also keep a set of diaries that only discovered posthumously somewhere late in 19th century that gave us his written confession.
IC:
As you know, 20th century investigations on the death of Wolfgang Amadeus Mozart proves that the high amount of Arsenic within his remains matches the confession written inside the diary of Antonio Salieri, his murderer.
While the murder didn't even get caught in his lifetime, and even Salieri later end up tutoring Mozart's son Franz Xaver Wolfgang Mozart in the arts of music (and from his diary he write this as the result of his guilt that he agreed to tutor him without payments). What resulted on this murder is certain, the world lost one genius in musical talents because of the others' envy.
Still some of their contemporaries actually did suspect the murder, but cannot really touch Salieri because of his closeness to the court and the Emperor, but still, 1830 play of Alexander Pushkin, "Mozart and Salieri" managed to shed some early light on this murder case (despite the artistic liberty taken by pushkin over his portayal of Mozart and Salieri).
So, what if Antonio Salieri actually managed to rein his envy and choose to not poison Mozart?