What does Huckleberry Finn do to make his father believe that he has been murdered?

I'm sorry, I think you have the wrong chapter number for your question. In Chapter Three, a drowned man is found in the river, and the townspeople believe is Huck's Pap. Huck is unconvinced after he hears the man was found floating on his back. He remarks that everyone knows dead men float face down, so this must have been a woman in man's clothing that looked like his Pap.