The American generic notion of "fair use" does not exist in Swedish copyright law. The current Copyright Act (which dates from 1960, but has been amended several times since) instead lists a number of exceptions to copyright which may or may not apply in certain situations; here are a few of them:
- Making temporary copies for technical reasons
- Making a limited number of copies for personal use
- Recording your own performances of protected works
- Making copies for preservation in libraries
- Making copies in Braille for the blind
- Quoting reasonable excerpts for context and critique
- Depicting buildings and art in public areas
... the list goes on. Some of these situations may be listed in the U.S. Copyright Act as well (I haven't checked), but for those that aren't, I suppose a defense of fair use could be tried.
So, if two people sharing a work electronically falls under the umbrella of "fair use" in Sweden, then there can be no contribution to a crime by the TPB guys.
As long as we discuss "two people", the relevant exception here would be private use (Article 12 of the Swedish Copyright Act). As has been pointed out by AC above, this is a bit hard to claim when someone makes copies for thousands of recipients. However, as the Bittorrent protocol may just as well involve thousands of people making one copy each for another person, I'd say this defense would actually have some merit, depending on other circumstances. If everybody is allowed to make a single copy, you can't prosecute a thousand people for doing exactly that just because the net result is the same as if one of them had made all the copies. Neither can you prosecute someone else for contributing to a collective act which itself doesn't constitute infringement.
However, this particular defense happens to be moot in the TPB case, because the prosecutor dropped the "contributing to the making of copies" charge already on the second day of the trial. The charge that remains is "contributing to making works available to the public", which is a different kind of infringement, and that does not come with an exception for private use!
This still doesn't mean the TPB guys will be found guilty, because it's the "contributory" part that seems difficult to prove. Making works available to the public, that's traditionally what a radio station may do, and the kind of "contribution" to that which would correspond to the Pirate Bay is to publish lists of radio stations, their frequencies and broadcast schedules free of charge. And one of those radio stations may actually be operated by King Kong in Cambodia, who hasn't even been called to the witness stand. Illegal or not? The court should tell. Will the World Radio & TV Handbook be next?