Answer: Antonio Salieri
The rumormill of the day was filled with stories of Salieri's poisoning of the great Mozart. These rumors are actually mentioned in Beethoven's conversation books. The entire movie is based on the assumption that Salieri's old age confession and alleged letter is truth. In fact, no proof exists to support the idea that Salieri murdered Mozart. Proof does exist that he resented him, was very jealous of him, and sabotaged his work, but no proof of murder. Facts: Salieri was frequently at Mozart's deathbed and attended his funeral. The "Requiem", however, was eventually completed by Mozart's composition student, Franz Xaver Sussmayer (recognize the youngest child's name?) who often accompanied Constanze to the spa at Baden Baden.