Police have said it wasn’t a robbery AFAIK
Wasn't there around 7 thousand dollars that HS withdrew from the bank that day that was not stolen?
Here is my hypothetical, which addresses both of these questions and how a payment (partial?) for the contract killer might have remained undetected. It is 100% speculation on my part and is extrapolated from the way I have dealt with my own emergency cash.
1. The Shermans decided to keep a large stash of emergency cash at their residence. They do so for reasons related both to refugee trauma and ordinary prudence.
2. The sum is large, at least a million dollars. This is because (a) the Shermans are extremely wealthy; (b) they may face risks that are unique to being extremely wealthy, such as kidnapping/ransom; and (c) for various tax reasons they may have an incentive to keep at least some money in cash.
4. This is purely a reserve and it remains untouched in the safe or other "safe" place. They don't use this reserve for pocket cash or even for larger cash spending (such as the money Honey withdrew presumably for holiday tips for her various service employees).
5. The Shermans tell Close Person (CP) about this reserve. They say (hypothetically), "In case something happens to us, there is a wall safe in the study behind the painting of the dog. The combination is your birthday reversed. There is a million dollars in cash plus our birth certificates, passports, and some jewelry." 6. The Shermans are not worried about CP knowing about the stash in the safe because CP has plenty of money of their own and will eventually share in their estate anyway.
7. CP hires an assassin to murder the Shermans. CP tells the murderer how to access the cash, which will constitute the fee, or a portion of it. The murderer does not steal anything else, such as cash or jewelry from the Shermans' persons.
8. When contacted by LE, CP says "Why yes, there was a wall safe in the study, but they didn't keep anything there except for their papers and some old jewelry, and as you can see all that is still there. So there certainly wasn't anything stolen from the house."
100 percent my speculation.
Facts that might support this: the urban explorer saw holes punched in the wall, leading to the theory that at one point there was a wall safe. The Shermans constantly had various service providers in and out of the house, and reasonable prudence suggests you'd want a safe place for even ordinary valuables.
Facts that might contradict this: For all their wealth, the Shermans didn't seem particularly security-conscious. Would they have had a safe? Would they have stored a large amount of cash?