Could have been something RB told her. He may have said he got tickets to Orient Express, when he never did & then told her they couldn't reschedule until late Aug (to buy him time). To me, Marion's trip sounds alot like JO's in the sense that there was no well-planned itinerary. She just traveled with a man who seemed to be in charge of the trip and made a lot of promises.
Separately, would be interesting to know if RB traveled back overseas right after he closed his security envelope in late October 1997. Did he use that as temporary but secure storage until he could personally take money etc. overseas?
I can't see RB spontaneously offering additional information that connects him to Marion (that Marion stored things at his home or that he went with her to the Southport school on an occasion), unless he needed to. I wonder if investigators produced some evidence he needed to explain away. For example, perhaps someone from Southport recognized his picture and remembered he had been there.
They have said from the beginning that this is an ongoing investigation. Investigating RB's crimes is probably the easier part b/c so many leads. Finding Marion may be much more difficult unfortunately.
It is really sad that this guy got away with this for so long---especially when he was on the police radar from as far back as 1969. Really disturbing that at no point did any investigator think to see if Marion's disappearance was connected to him. I sure hope Sally feels some level of vindication & accomplishment. Think of all the victims (including the two witnesses) who could have been spared this trauma had the system taken Sally's concerns more seriously. At least she has helped expose this despicable human.