Who does Pünd accuse of Magnus' murder in the novel, Magpie Murders?

Pünd accuses Robert of having killed Magnus as well as his younger brother and his younger brother’s dog. Pünd believes that Robert’s mother knew there was something wrong with him from the time he was born - that he had the willingness to kill to get what he wanted. Pünd believes that Robert killed Tom because he was jealous that the younger boy had found a treasure Magnus had hidden for them. He also believes that Mary witnessed the murder.