people at my school really just dont cheat it seems like. We have a strict honor code, great/friendly curve, and a high tuition, so noone risks getting kicked out to cheat. If it is closed book, there is a significantly greater chance that he is probably cheating rather then just bored like when I leave. However, straight up, you probably know the material as well as he does. Also, the time he lost makes a huge difference in his ability to perform anyway. So, even if he was cheating, it was a minimal benefit to him in the context of knowing more information then you guys and it took away his time.
you obviously cant say anything if you dont see it. But, I wouldnt stress it. People suck. I hate to do that spiel but there are cheaters all throughout the legal profession and there are plenty of people that got where they are without earning it. If he is willing to risk getting kicked out for a minimal benefit at that, more power to him, cause it is not worth the risk to me.