> The reason I tend to believe this scenario is because it's completely consistent with their behavior.
Another reason to believe this is that it is something that has happened often in the past before modern banking regulations. Seriously, read history of banking in Netherlands or England, the idea:
"Oops, I just lost my customer deposits. I'm probably going to get lynched now. But hey, if I just hide this until I make the loss back from fees/reckless trading, I'll be able to pay my customers back and avoid being lynched. It's a win-win."
Is something that at least hundreds, if not thousands of bankers have had over the course of history. As far as we know, it never works.