Special correspondent Oscar Swartz reports.

STOCKHOLM — Prosecutors dropped half of the charges in the landmark trial of The Pirate Bay file sharing site Tuesday, leaving observers stunned and prompting questions about the government’s preparedness in the long-awaited criminal proceeding.

"I will drop all charges that relate to producing infringing copies and will hence restrict the prosecution to the act of making works available to the public," prosecutor Hakan Roswall announced at the opening of the second day of the trial. "When I talk about making something available to the public I mean making available torrent files."

At an intermission, Roswall refused to clarify the change of heart to reporters. "As you can see I have a lot of other things to think about," he said. "There will be new adjusted charges distributed on paper tomorrow, Wednesday."

Four men associated with the defiant BitTorrent tracking site are on trial for contributory copyright infringement. Hans Fredrik Neij, Gottfrid Svartholm Warg, Peter Sunde and Carl Lundströmface face up to two years in prison each, in addition to fines as high as $180,000.

The Pirate Bay’s supporters quickly claimed victory in the blogosphere, and many expressed astonishment at the course-correction. This was, after all, supposed to be the seminal piracy prosecution, with Hollywood throwing the kitchen sink at a few defiant Swedish computer nerds.

Peter Danowsky, the attorney representing the music labels, downplayed the reduction in charges.

"It’s a largely technical issue that changes nothing in terms of our compensation claims and has no bearing whatsoever on the main case against The Pirate Bay," he said in a statement. "In fact it simplifies the prosecutor’s case by allowing him to focus on the main issue, which is the making available of copyrighted works."

The move is remarkable because of the extensive groundwork the content industries and the prosecutor has laid for the case. The Motion Pictures Association and other plaintiffs had collected evidence for many months by participating in file-sharing torrent swarms, dumping screenshots of downloads in progress and collecting information before the raid on May 31, 2006, in which 195 computers were trucked away by the police. The prosecutor led an investigation for two-and-a-half years after that.

The prosecution has specified 21 works of music, nine movies and three computer games that were allegedly infringed. The Pirate Bay defendants were not charged with direct copyright infringement, but only in assisting in committing such acts. Under Swedish law, prosecutors must therefore prove the defendants engaged in "facilitating for other people to make available a copyright protected work via transmission on the internet" in a specific file on a specific date.

The hitch in the prosecutor’s plan hinges on Pirate Bay’s dual-functionality. The site includes a "tracker" that coordinates communication between peers downloading and uploading files. But it also has a searchable index that merely lists the torrent files available through a variety of trackers, not just The Pirate Bay’s. The prosecutor now appears to agree with the defendants that he cannot prove that the specific files at issue were handled by Pirate Bay’s trackers.

The only thing that is left is "assisting making available" the torrent files, a charge that the prosecution evidently hopes to press based on Pirate Bay’s index alone.

The move may have been prompted in part by the defendants’ opening statements. On Monday, Pirate Bay co-founder Fredrik Neij discussed so called "trackerless torrents," which use a Distributed Hash Table, or DHT, and don’t rely on a torrent tracker at all.

"We believe he dropped charges after having googled all night about DHT," an upbeat Peter Sunde, one of the defendants, told Wired.com later. Fredrik Neij and Gottfrid Svartholm Warg boasted that they were just scratching the surface of the flaws in the government’s case, and that they would raise deeper technical points later in the trial.

It remains to be seen whether facilitating making torrent files available is enough to commit the criminal act of assisting in copyright infringement.

"Absolutely not," claimed Rick Falkvinge, the leader of The Pirate Party. "If they can claim that facilitating for others to publish a torrent file, which contains no copyright protected information whatsoever, then this shows that they want to shut down the internet for good."