The term SCARPIA'S KILLER is solved by the crossword solution TOSCA, which is a five-letter word. Tosca is an opera composed by Giacomo Puccini and first performed in 1900. The opera follows the story of Floria Tosca, a singer who kills the villainous Baron Scarpia in revenge for his murder of her lover. Therefore, the crossword solution TOSCA is referring to the character of Floria Tosca, who is the killer of Baron Scarpia.