What was the motive behind the alleged plot to kill Alfred Ruff's wife?

According to the case presented in Crime Fix, Alfred Ruff claimed that there was a conspiracy involving two women (his wife's daughter and a friend) to kill his wife, Lisa Bishop, for insurance money. During police interrogation, Ruff stated that his stepdaughter became angry and decided she wanted to kill her mother by poisoning her with an unspecified substance. The alleged plan centered around financial gain through collecting life insurance benefits following Lisa Bishop's death.