It is unknown precisely what law enforcement has done with the legal files stored in the Megaupload platform.
Privacy Protection Act
US law enforcement must be mindful of Privacy Protection Act ("PPA"), 42 U.S.C. § 2000aa:
“[I]t shall be unlawful for a government officer or employee, in connection with the investigation or prosecution of a criminal offense, to search for or seize any work product materials possessed by a person reasonably believed to have a purpose to disseminate to the public a newspaper, book, broadcast, or other similar form of public communication...”
Essentially, the purpose of the law is protect First Amendment free speech, free press materials.
What is less clear is what police may or must do with PPA-related material after they have lawfully seized it. In Steve Jackson Games, Inc. v. Secret Service, a district court penalized the government for not returning PPA-protected materials promptly after learning they were protected.
Asset Forfeiture Law
Another relevant law is the 2000 Civil Asset Forfeiture Reform Act, which is intended to make it easier for innocent parties to recover their property when seized by the US government. A public-interest expert in holding government to this law is the Institute for Justice. The Institute for Justice should consider taking up the case for innocent Megaupload users.
Related: Megaupload Raid: The Legitimate Users