Why isn’t the defense in the Rutgers case permitted to know who the other guy was?

The identity of the gay man who was secretly filmed via web cam in an intimate encounter with Tyler Clementi, who later killed himself by jumping off the George Washington Bridge, is being hidden by NJ prosecutors.

The defense claims the unknown man has information that will help their client but they don't know his name. It just seems strange and odd. As much as I don't sympathize with the defendant at all in this case, it is weird not permitting the defense the chance to interview the other guy involved in this entire thing. I certainly don't believe the unknown man has anything to help the defense but let them at him. In fact, maybe he will end up suing the defendant for invasion of his privacy as well.