Those documents were illegally obtained and Grisham and his half-baked gang need a legal whack on the nose for that if nothing else.
The school should also busted on this one for allowing them access to private files.
If he was so bothered by the source of the letters then he's certainly got the bucks hire a real PI to look into things properly.
And oh--hey--there's the cops--they're available.
And reporting it to the Post Office wouldn't hurt. I think such harrassing mails are a Federal crime.
If some jerk is slipping notes under doors you can get a "Nanny cam" to catch the perp. Then you turn what you found over to the cops.
If something is private and confidential you use a court-order not the freakin' Ant-Hill Mob and Chugga-Boom.
Once the legal dust settles, he and his pals need to write a
groveling letter of apology to the lady.
And it needs to be in the local paper.