The blonde copper killed her because he believed Hattie had put a curse on him. The little heart she had planted wasnt a curse but only worked because he believed it did. His wife found the charm and hatties hair and planted it on Linus's dad and then told the police that he had done it, to cover up for her husband; 'nothing is more important than this family' even if you are married to a murderer!
Assume somehow Linus managed to switch the evidence that was planted for a rock so his dad got off - well someone did that!
Caitlin, Hatties Twin dressed up as Hattie, she suggested that she was guiding her with what to do, and she pointed out who had been responsible (the blond copper) VERY frustrating we didnt see him get arrested! Or that we didnt see exactly what had happened to Seth (although the blood on the tree stump was a big hint that he'd been killed)