I learned about https://en.wikipedia.org/wiki/Assassination_market in the early 2010s. It wasn't phrased like a prediction market focusing on when a person would die, but more like a bounty. If the bounty/pot got big enough, eventually it would be worth it for someone to do it.

Even thinking/writing about this now, it still makes obvious sense and I'm surprised it hasn't been seriously made yet with crypto: if there's a pot of billions, contributed to by millions, the incentive becomes not just about the money, but the adoration, protection and power that would come with doing so many people a favour.