Sam Westing's death is confirmed by what?

Westing's death is not confirmed in Chapter two, but Oris Amber tells the following story;

“Naw,” Otis Amber, the old delivery boy, answered. “Nobody’s seen him for years. Supposed to be living on a private island in the South Seas, he is; but most folks say he’s dead. Long-gone dead. They say his corpse is still up there in that big old house. They say his body is sprawled out on a fancy Oriental rug, and his flesh is rotting off those mean bones, and maggots are creeping in his eye sockets and
crawling out his nose holes.” The delivery boy added a highpitched he-he-he to the gruesome details.