I'm more interested in T/DoD (time and/or date of death) markets.
Obviously only people who make it into the public eye for outrage and wrongdoing would be cool considered as serious targets, as they would accrue a serious amount of bets.

This way the people betting aren't outright paying for the murder of a certain person..
And the person who wins and is proven to be rite isn't necessarily the killer (or cant be proven to be).

Might make for a who lot more of a polite society and a fair and just government... maby not many bets would be being placed in the end once the market is set up, and the first few obvious targets met their fate.