I'm on the view that RB didn't need Marion to return to Australia because everything he did once he returned could have been done by a person posing as Marion under his directions eg DdH. I think he found a woman in Europe (or simply an accomplice) who was willing to pose as Marion on the flight using Marion's Remakel passport with her own photo. He has had a habit of leaving women stranded so that's what he did - whether he told her or not that he was returning to Australia or had an accident and was in hospital, it doesn't really matter. But I think it is likely that Marion didn't even know he was returning to Australia. Perhaps RB was the one who bought Marion's airline ticket and he forged her handwriting on the incoming passenger card which he had saved up from a previous trip and gave it to his accomplice. I still think that Marion told Sally she would not be hearing from her for a while is because she was looking forward to meeting RB's (accomplice) friends - Maz and the Dutch dentist - and going to Amsterdam with them re one of her postcards but MB met her demise at the hands of the Dutch dentist and Maz took the flight.
Now with Marion out of the way, RB could proceed with his scam in Australia without the fear of Marion returning unexpectedly.
The usual reaction to his buying another car is that RB could have used it to transport MB's body. His story was that it was for his daughter to drive but she was too young then to drive. I have assumed that he could have bought the car to enable him to conveniently tie up loose ends eg sell Marion's items on Gumtree or The Trading Post and deliver them to the buyer, get him and DdH to the bank each day without worrying about being seen on public transport or having the cash stolen, nobody would recognise him/them in the new car, and going to Grafton and so on.
Like many other people here now I just cannot imagine MB surviving with him here from August to October without becoming suspicious of him and phoning someone especially if they were not together 24/7 which isn't his MO. I have never seen RB as a murderer but I wouldn't put him past hiring someone else to do his dirty work. I also cannot see him selling organs to Japan.
So why check the liver? It appears that most of his victims have been over 50 and would not necessarily have perfect livers so he would be hoping that their liver is damaged and if someone poisoned them with a poison which does not leave a trace, their death could be put down to liver disease.
I thought similarly to yours when I first heard about this case. I thought MB was killed in the UK.
Here's my theory now.
I always thought it was odd that Marion told Sally she wouldn't hear from her for some time after having sent loads of communications over the first few weeks of the trip. On such a great trip, MB would have continued to check in. I think RB told her they would get married and live in Europe. She didn't want to tell her family about it until it was done. They couldn't object or talk her out of it if the deed was done. She knew what was she was doing was sketchy but didn't want anyone to tell her no. Many of his victims did this and other women who are conned.
Given RB's previous cons when he left the woman and returned to Australia. What if RB abandoned MB in the UK with no explanation? Unlike he did with the other woman, leaving her with her relatives. Still, under the assumption they were already or going to marry, she returned to OZ. Thinking she could contact him and sort out whatever the issue was. He loved her, and they would live in Luxembourg. Happily Ever After. MB didn't want to be divorced again. Think of her shame. As with all of us, she couldn't imagine that RB would be such a con artist. She assumed there would have to be an explanation for why he'd left her in the UK. She checked into a hotel and decided she try to find RB. When she began researching him, she realized that RB wasn't what he seemed. What if she found his home and turned up? This would explain why he claimed MB came to his house to pick up his her stuff. If the police found her DNA there, that would explain it. Having MB turn up his house with his wife and family finding out could ruin his whole life. Is it a motive for murder?? He couldn't have people find out. He kills her. Once he's killed her, he takes her purse with her ID and bank cards. This is how he pays for his son's car. If he takes out the minimums, he doesn't think anyone will notice and ask for ID.
For the time between August and October-what if he groomed a woman who looked like Marion to take out the 80k? He would have cleared it if he knew how much money was in the account. If the person posing as Marion couldn't ask, she should know. Maybe part of the story was that she would say she was moving to Bali to throw them off. Maybe RB has promised this woman they would move to Bali with the money? This is what he does. Promises new lives to lonely women. Women he's been involved have done things that don't make sense. He'd been controlling his wife for years, so it doesn't seem far-fetched. He also got Marion to lie on her landing cards and they thought her to be an honest person.
I know it doesn't fit in with his normal con, but potentially he'd never had a woman turn up at his house and threaten his lifestyle. When people are pushed they do some desperate stuff.
Many people believe the wife and family had to know and I don't want to believe it. People in these sorts of controlling relationships are kept in the dark. The woman on the stand looked as big a victim as I could imagine.
Poisoning is a non-violent way to kill someone. I'll be interested to hear what they find out.
I watch a lot of true crime. Having your secret life exposed is often the reason for murder. People have killed for much less.
Of course, this is just one of many theories.