Complex sentence: Leoncavallo claimed that he based the story of "Pagliacci" on an incident from his childhood: a murder in 1865, the victim of which was a Leoncavallo family servant, Gaetano Scavello.
Split into simpler sentences: Leoncavallo claimed that he based the story of "Pagliacci" on an incident from his childhood. This was a murder in 1865, in which the victim was a Leoncavallo family servant, Gaetano Scavello.