Earlier this week, we reported that the RIAA had decided to drop a long-standing copyright infringement case against Joan Cassin. Now we know why: in an e-mail to Ars, the RIAA revealed that it no longer believes Joan was the person on the PC that was allegedly sharing copyrighted music, but that it was someone in her house.

As a result, Warner v. Cassin has been replaced by Warner v. Does 1-4. Why the Doe designation? The RIAA still doesn't know who the alleged copyright infringer was, and needs the court's help to uncover the offender. In its new complaint (PDF), the RIAA says that while Joan Cassin denies that she infringed on the record labels' copyrights, she has failed to finger the culprit. "We recently uncovered evidence in the course of the litigation that another member of Ms. Cassin's household is likely the infringer," RIAA spokesperson Cara Duckworth told Ars.

In his coverage of the new complaint, copyright attorney Ray Beckerman points out that the new lawsuit has been assigned to a different judge and that the RIAA is treating this as an all-new case. In a letter (PDF) to Judge Stephen C. Robinson, Beckerman (who is one of Joan Cassins' attorneys) asks him to recall his order dismissing Warner v. Cassin without prejudice. Instead, the previous case should be dismissed with prejudice, which would mean that the RIAA would be barred from bringing this new case.

As one might expect, the views of the RIAA and the defendants' attorneys on how the case should be treated vary widely. The RIAA is treating this as a brand-new case and claim of copyright infringement, and the new complaint makes no mention of the previous lawsuit. Beckerman, on the other hand, sees this as the third lawsuit filed over the same claim. In a conversation with me on Wednesday, he explained that the RIAA's dismissal of Warner v. Cassin should have been with prejudice, since it's the second time the RIAA has dismissed the same claim (the first being the original Doe lawsuit the RIAA filed to learn Cassin's identity). Cassin should therefore be considered the prevailing party and entitled to an attorneys' fee award.

Beckerman is also asking (PDF) the new judge, Charles Brieant, to refer the new case back to Judge Robinson, pointing out that the RIAA walked away from the last case while a motion for dismissal was pending. His letter to Judge Brieant accuses the RIAA of "forum shopping," trying to make an end-run around the pending motion for dismissal, and trying to begin discovery (to learn the identity of the alleged infringer) in spite of Judge Robinson's stay.

How the new case plays out depends on how the judges view the assertion that all three of these cases are essentially litigation over the same copyright infringement claim. If so, then it seems likely that Judge Robinson might consider his previous dismissal and say enough is enough. The RIAA's new complaint certainly appears to be closely related to the original Warner v. Cassin and is seeking the same information that it was unable to get in the last case due to the judge's staying of discovery.