Jean-Marie Leclair was an unsolved murder mystery of the 18th century. He should not have been known for that. He founded the French school of violin. But he was stabbed in the back and neck 3 times, killed in the vestibule of his own home in 1764. He was a great violinist and composer for King Louis XV of France. No one was ever arrested, not Louise Roussel, his ex-wife, who did the engraving of his compositions for him, and not the envious nephew,...