Assuming this is a tournament and not a cash game, my initial reaction, based on the limited information you provided, would be to declare both hands dead and return the chips wagered to the appropriate parties. I would also be inclined to give the player that initiated the fold (the player who folded his cards on top of his opponent) a penalty and a warning to the other player for not protecting his hand. This is predicated on the whole hand being played 'heads-up' from the deal.
This said, there may be any number of facts that could change the above. If, for example, there had been some prior 'history' between these two, or if one was significantly more experienced than the other I very well may rule differently and award the whole pot to one or the other. It all depends upon the facts applicable to the situation.
What you presented was very general and it is very likely there are other facts that would need to be included.