General Discussion

Something happened to Mrs. Guthrie. It might never be solved not unlike Jimmy Hoffa.

I, too, suspect she died accidentally and the perpetrator(s) has covered it up. Probably a robbery that went bad somehow. The perpetrator might not have even known her daughter was famous.

Usually, the simplest explanation leads to the truth. Complexity requires too much messiness.

ETA: imagine the perpetrator’s discovery that his victim was related to someone famous! They must have had a cow!