This is also true with traditional stock markets, except that laundering real money is much harder to do alone. In the real world an assassin can't really involve more people as those people would realize they are loose ends since they have a get-out-of-jail card in turning on you.
The markets could get ahead of this by stipulating that a resolution via murder will always lead to resolution at prices at a time prior to the death. This would technically incentivize a potential assassin to commit a deniable murder, but if they succeed it won't be the market's [PR] problem.
Before the Iran bets there was a suspected Google insider who made $1.15M on Polymarket (22 of 23 correct bets in 24 hours) and Israeli soldiers criminally charged for monetizing classified intelligence on event contracts.
Textbook Akerlof: without enforcement the adverse selection spiral kills these markets before they get a chance to prove useful. I tracked all three cases here: https://philippdubach.com/posts/the-absolute-insider-mess-of...
"Last summer one “ricosuave666” won more than $150,000 on Polymarket, a betting platform. Their true identity was not clear, but the source of the winnings was: ricosuave666 had bet, with suspicious accuracy, on the precise timing of Israel’s attacks on Iran."
So, these people can be found. Overall however, the magazine does not think that these markets should have a blanket ban.
[1] https://archive.is/W8Ga8 (Prediction markets are rife with insider betting)
A new Polymarket account made over $500k betting on the U.S. strike against Iran