Haram and Halal

I was working with a Jordanian Colleague today when one of his friends came in to see him. A short discussion was had where he produced an envelope which he gave to this man with what turned out to be $5000.00 Riyal. Asking him about this he explained that a group of nine friends got together and each month they collect up 5000 riyal and they take turns receiving 40000 riyal. I talked to him about doing same thing but putting it in the bank and paying it out at the end of the month. Simple economics would mean you would always have a 40000 deposit and so you would generate interest . He said this was Haram. Haram is Arabic for that which is forbidden. I’ve written about it before but I thought it covered only things like murder, adultery and the like. As opposed to Halal, that which is good. We tend to think of halal as relating to food only but it covers far more.
I think what he was saying as to why it was haram was that you are taking advantage of an opportunity. So no banks , no interest just a big payout once every nine months. I sort of compulsory savings scheme with no extra benefits. He was just thinking about what he would do when his turn came.