Ghosts (spoiler)

1. Who actually stabbed Josh Tate to death in this story? According to Spencer Foster he had an arguement with Josh and killed him accidentally, but it was mentioned earlier that Josh was killed by a single stab wound, so who stabbed him on earth? Was it Spencer or his parent?
2. Who attacked Liam Fallon in this story, was it Martin Hexton or someone else? That was never made very clear at the end.