Even if Reardon turns out to be be wholly innocent, I find that a highly questionable statement.
They are madly in love.
They live together.
Reardon says he has never been happier in his whole life
He's going away for a whole weekend.
They presumably both have mobiles. They can text each other. Did he not even send a text?
I am looking at that statement again: "...it wasn't unusual for Jo not to answer the phone".
Certainly puzzling, that one.