Showing Blood from a Stone by Donna Leon

On a cold night shortly before Christmas, an immigrant street vendor is killed in Venice's Campo Santo Stefano. The nearest witnesses to the event are the tourists who had been browsing the man's wares before his death - fake handbags of every designer label - but they have seen nothing that might be of much help to the police.

When Commissario Brunetti arrives on the scene, he finds it hard to understand why anyone would murder an illegal immigrant. They have few social connections and little money; in-fighting among them is the obvious answer. But once Brunetti begins investigating this unfamiliar Venetian underworld, he discovers that matters of great value are at stake in the immigrant community...