I am absolutely loath to admit this in public, but I agree with Taft2016 on this one. Cops aren't stupid -- if they're looking for guns and they see the seal of a major government security agency on the top of a piece of paper, they are in every way allowed to continue reading and, if they find the papers suspicious in context, take them. It might suck for the press lady, but until it's established that she's using those documents in her role as a journalist and not as a spy/terrorist/whatever, they're potential evidence.
If they keep the papers once that potential criminal charge has evaporated, well, that's bullshit.