Bill and Steve would meet in a plane flying over the ocean - in order to prevent anyone else being involved and to prevent any monitoring. And, in general, these deals made them very rich, so the only people who could betray them had both made a lot of money and been involved in illegal activities themselves. Kind of hard to see much risk in something that is completely deniable. If I hadn't spoken to people with direct knowledge of these things, I wouldn't know it myself. I'm not sure what it would take to get people to admit to their involvement.