> if the perpetrator could cover their tracks, the potential would be much greater than 6.5 billion
I think it's interesting to consider that this already could have happened or could currently be happening. A sophisticated attacker may be quietly reaping rewards in such a way that it's going unnoticed.
Granted it's unlikely given Bitcoin's core design is to prevent exactly that kind of untrackable-bad-actor-behavior, but it's absolutely possible with known weaknesses like a 51% attack.
I would hope some of the parties heavily invested in Bitcoin have verification tools that monitor the mempool vs. what ends in the Blockchain as I think even the most subtle attacks could be discovered that way... however even that may require an impossible perfect knowledge of the global mempool at any point-in-time.