This would only apply if the existence of a Pirate Bay account were the impetus for the investigation. There is just as much a possibility that the driving fact

This would only apply if the existence of a Pirate Bay account were the impetus for the investigation. There is just as much a possibility that the driving factor was the observation of your IP obtained through a standard torrent client. In your example, the IR evidence was the grounds by which they obtained a warrant. I'm not saying this wouldn't be the case in our hypothetical prosecution here, but the distinction is important. The bottom line is that suing individual file-sharers is an inane idea to begin with. The RIAA/MPAA are using this only as a shock & awe tactic. The rolling back of the file sharing tide will not come from the direct prosecution of every file-sharer. Their hope is that many people will become fearful of prosecution, thus resulting in a reduction of piracy.