The Brother changed the orders put in by some scammy front-runners in a completely dodgy 3-card-monte market, so that the scam artists got left with 25m of things that the scam artists has bought as part of their scam. Only the things aren't worth 25m anymore, the scam artists got scammed.
It appears that crypto front-running using inside information is legal at one level of the market, and insiders pay to play in that market, it's supposed to balance out in a free-market kind of way, so it's not actually a scam, it's a user-pays market
But in this particularly illiquid market, that free-market balance doesn't work, it's a total scam, and when the market is subverted, the legal scam artists suddenly loose instead of the Brothers.
The Brothers are being prosecuted for wire fraud, not for stealing.