This is the reason why I have the theory he used MB to help hatch a plan for his future prospects with his 'singing testicles' lover.
Somewhere in all this is MC and her reasoning for producing all the correspondence that was so damning to him at the inquest.
Their friendship was years long. They were still corresponding even when the DeH's had moved to Tasmania - this was years after she looked after '"a little boy who looked like frederick" and says she stopped the relationship when she found out he was married

.... yeah right.
IMO he hatched a plan to swindle FR with the help of MC and used Marion as the scapegoat. Somewhere along the way it all turned to *advertiser censored* and MC had to find a way out of a disaster so she set up to out him and remove herself from any potential criminal activity. That letter was used to embarrass him and let everyone see he had used her too.
She played him at his own game. Neither will implicate the other now