A lawsuit from a few years prior to the events of the book reveals that Mr. Hoo had interactions with Mr. Westing.

The first time that readers learn about the lawsuit is in chapter 4, but no information is given about who was suing Mr. Westing. Chapter 4 begins with Turtle Wexler going into the mansion prepared to stay all night and come away with a lot of money from the bets. She rushes out before fifteen minutes pass, because she saw a corpse. The next day the newspaper has an article about Sam Westing being found dead. The article gives Turtle some details about his past life and makes a brief mention that Westing was sued by an inventor:

Five years later he was sued by an inventor over rights to the disposable paper diaper.

Readers will find out, along with Judge Ford, who the inventor was at the very end of chapter 9. Judge Ford has been trying to figure out the Westing connection of many of the people in the building, and chapter 9 has a newspaperman calling her up with information that he found. He found information about an engagement announcement between Angela and Deere, but he also found "several clippings" about a lawsuit against Sam Westing. The newspaperman confirms that the lawsuit was brought against Westing by Mr. Hoo.