US authorities arrested a soldier involved in the capture of former Venezuelan President Nicolás Maduro who allegedly bet on the operation’s outcome before it took place, amid growing fears of illicit betting in prediction markets.

The special forces soldier is accused of making upwards of $400,000 from betting on the outcome and timing of Operation Absolute Resolve, which the US Department of Justice said was evidence of “clear insider trading.”

Experts warn that prediction markets are stoking corruption in the US — hundreds have placed successful bets on key events in the Iran war, The New York Times reported — fueling growing calls for Congress to regulate the marketplaces to prevent officials from profiting from privileged information.