The U.S. Postal Inspection Service supports and protects the U.S. Postal Service and its customers by enforcing the laws that defend the nation’s mail system from illegal or dangerous use.
What do they have to do with ebooks??
What do they have to do with ebooks??
I think legally they can investigate whatever (alleged) crimes they want – subject to the outcome of any turf wars with other government agencies. Their official purpose may be to investigate one particular category of crimes, but it is unlikely any court is going to throw out a prosecution because the "wrong" agency gathered the evidence. Government agencies are frequently trying to expand their empires, move into new areas, prove their continuing relevance when faced with technological changes that undermine their original reason for existence.
At the extreme, you end up with agencies whose names are purely historical and have nothing to do with their current functions. A good example of that is the Railroad Commission of Texas, which no longer has anything to do with railroads–now it is the Texas state regulator for the oil and gas industry (and also surface mining for coal and uranium). I don't know why they don't just change their name to "Texas Oil and Gas Commission" or something like that. One reason, of course, is that they don't actually control their own name, the Texas State Legislature does, and it seems it likes their name just the way it is.
Also, even supposing a criminal investigation was in violation of the appropriations laws (money appropriated to investigate one type of crime being illegally redirected to investigate another type of crime instead), that (as far as I know–IANAL) isn't an issue the accused has standing to raise in court.
A (possibly) real example of this happened under the Clinton and Obama administrations, when Republicans in Congress tried to appropriate money specifically to prosecute adult pornography, and the Justice Department (allegedly) illegally spent a lot of it on child pornography prosecutions instead. But even supposing the allegation is true, it was of no legal benefit to the accused.
I haven't seen the court filings yet, but I guess that a unauthorized (by the publisher) physical reproduction of a book (that was domestically sent through USPS, otherwise it'll be under US CBP) that just so happens that the source for the PDF used for the physical reproduction is from Z-Library.