Otis seems to be a delivery boy with a low IQ. Remember, though, everything's not as it seems in this book; he's actually a skilled private investigator on a long-term retainer. Sam Westing hired him for a decades-long gig, simply to keep track of the ex-Mrs. Westing and make sure she didn't get into trouble. Yet in his long-term job caring for the woman we know as Crow, he falls in love with her and they end up getting married – and running a soup kitchen. Otis is a great secret keeper; when Judge Ford hires him to investigate the other tenants, he never gives up the information he knows about Crow. It's "privileged." For that matter, Judge Ford's also a good secret keeper, as she doesn't reveal Otis is the P.I. until the trial scene.
Weirdly, many of the characters come to think their clues point to Otis for the final reveal, although only one team puts him forward as their final answer. Judge Ford and Sandy wonder if Otis is Sam Westing, but abandon that plan when they learn he didn't have plastic surgery. Theo spells out "otis" from his clues, but doesn't see how a man who volunteers at a soup kitchen could be a murderer. Sydelle and Angela think his last name, "Amber," is an important clue when they put the other clues together and come up with "America, the Beautiful"; Sydelle suggests him as the answer at the second will reading. Several characters also suspect him of being the bomber. He ends up as a potential scapegoat for much of the book.