I think that Josie Jo Ford is the one who killed Sam Westing. She possibly killed Sam because he would refuse to pay the unexcepted payments she would give him. She keeps information to herself and her secretary. I also noticed that she hurried back in side when there was nothing to run from. She was not wanting anybody to find out about what she said about Otis Amber when everyone says the same about him. There was no reason to hide that so she might have started the rumor of Otis killing Sam while knowing that she killed Sam. Later on in the book I figured out that I was incorrect. Come to find out Sam was not dead. He was in disguise as different people. He took on disguise of Sam Westing, Barney Northrup, Sandy McSouthner, and Julian
