You are referring to a court using materials or a third party making derivative works from such sources.
Both
The court may have an exemption to copyright to provide the entire work (or it may be reduced or redacted).
It cannot be reduced or redacted once submitted into evidence, there have been a variety of copyright lawsuits around that, and there is a fair use exemption for the portions of work that make it into a lawsuit. So you cannot sue the people submitting it or the court or the people requesting the case files. The judge typically will not allow an entire book to be submitted into evidence, only relevant portions, so it is very rare that you will find an entire copyrighted work in a case, often you'll only have pictures of it, they'll be modified or redacted before being allowed into evidence.
However, the sources themselves do not fall into the public domain and a third party can’t just re-publish the entire source (not a derivative work) and sell it
That's not what I said. The sources remain under the copyright of the owner, the case files fall under fair use. You can republish the entire case and derivatives of everything published in a lawsuit, that is what companies like LexisNexis do.
You can however, probably (not sure if there is case law about this) not sell the case files as being the book itself published by the author, that would be falsifying the brand/name, but that isn't a copyright issue. You can't sell other revisions of the book if they weren't published in the case. You can publish the "author vs. state" case and include all case files, if that happens to include an entire book, then that is fair use, because the judge thought it was relevant to the case to submit it into evidence, you can't redact it after the fact, as then you could redact pretty much anything people didn't want to be public, such as e-mails, letters etc nor could people learn what the relevant factors in the case were.
In the case of child porn for example, or the description of a murder you did yourself, those things aren't copyrightable or have any privacy attached, anything you create in the pursuit or progression of a crime is not protected by copyright or corporate secrecy or patent law or whatever else they may claim. This may be the case here, if the elders wrote down or recorded the proceedings of a meeting in which they colluded to commit and/or cover up a criminal act such as child molestation, there is no protection at all on those documents, it is in the best interest of the public for those documents to be revealed to the public.