I am not an expert! But seems to me that in most countries that I know of, that if nothing is on paper than it is not legally binding. Your friend could do a few things, first he could go to the could make his case that he was just an employee who was not paid. since there is nothing to make the case on partnership, however I know that in some countries if an employee keeps a log of all their hours and along with a letter from a few customers that they served that the employment standard board will take their side. Secondly, if your friends passport is being held illegally by these bumsters than your friend could claim that his passport was stolen by these men and have it replaced. finally your friend could take his case to court as is, he still has a good chance of winning money from these guys if he can prove that he put money into the business regardless if there is anything on paper or not.

Good luck!