why does susies father become suspicios of mr harvey ?

Jack knows that Harvey is guilty of murdering his daughter, but he can't prove it. Susie's messages to her father get all jumbled up in his anger; he sees things that aren't real, and he can't see the things that are. Jack can see Harvey's guilt in the way he looks at him, and he's sure of it after the way he reacts when he helps Harvey build the tent.