Capitol Records' lawsuit against used digital music seller ReDigi could well determine whether consumers who purchase tracks through iTunes, Amazon or other digital sellers have the same right to resell them as people who purchase CDs. The answer to that question is increasingly important, since people are buying more and more media in digital form. Given the stakes for consumers, it's not surprising that an outside watchdog wants to weigh in on the case. But U.S. District Court Judge Richard Sullivan seems convinced that he can decide the far-reaching legal issues without any outside input. Last week, in a terse one-page order, Sullivan turned down a request from the digital rights group Public Knowledge to file friend-of-the-court papers. Public Knowledge sent Sullivan a letter on July 27 asking for permission to argue that ReDigi's platform doesn't infringe copyright. The case turns on whether consumers have the same "first sale" rights to digital music as they do to physical property, like CDs. The first sale doctrine allows people to resell any property they legally acquired. The problem is, it's difficult to apply that doctrine when the property is digital and needs to be copied -- even if only fleetingly -- before it can be sold to someone else. ReDigi appears to do so (though the company officially says it transfers the "original" file from users' computers to the cloud). Semantics aside, here's how ReDigi works: The company scans users' hard drives for proof that they acquired music legally, and then allows users to upload their tracks. ReDigi then deletes the music from users' hard drives and allows people to resell their tracks But that initial act of uploading seems to involve making a copy -- which Capitol says infringes copyright. Public Knowledge wanted to weigh in against Capitol. Among other arguments, the group says that ReDigi enables consumers to exercise their first sale rights and, therefore, the platform is protected by fair use principles. "Transferring the ownership of digital files should fit squarely within the bounds of fair use," Public Knowledge argues in its letter to Sullivan. " The public interest in allowing consumers to transfer ownership of their own digital files far outweighs any potential harm to the holders of copyright in those files." Given that this decision could have a profound impact on consumers, it's unfortunate that Sullivan decided that he didn't want to hear from a watchdog who represents their interests.