Surely the post office or P.O. box type business can assist in figuring out who mailed them? I would think a mass mailing that large doesn’t go unnoticed. Those responsible might have even been dumb enough to get all that crap printed somewhere. The part about cricket fields is kind of random.
How can you even mail stuff anonymously in 2017?
I’d say it’s still pretty easy to mail anonymously. My family got mailed white supremacist literature via USPS, we handed it over to the cops, and… nada. It’s been years. I’d be more interested to know if any hidden copier or printer codes are buried in those images. We’d probably have a better chance uncovering where those were produced than where they were mailed. Also, I know a postal inspector. It’s all about people mailing drugs, so the resources are already committed elsewhere.