If the same thing would of happened where i live, this is what would happen.
FIRST, Whoever OWNS the property they were found on would be the owner of the property that was dug up IMO.
Second, I would think the only person or agent of the company that owned the property would be the only ones who could authorize anyone to "take" what was found.
Third, in my agency, even if LEs were given permission to take the property, we couldnt take it cus it would violate agency policy to take gifts worth over $25.
If the owners of the dug up property gave permission for whoever to take the stuff and it didnt violate any kind of agency policy, i dont see any wrong doing IMO. Now IF the owner of the property DIDNT give permission to take the stuff and wanted it back, then i could see a problem.
Personally, i doubt that any agency would have their civil attorneys look into the legalities of this being that it has nothing to do with LE activity. Lawyers get paid to do this kind of work and i would be surprised if tax dollars were spent to look into if some LEOs could sell something outside the scope if their duty for private business! I also doubt that LEOs that knew nothing about these would of contacted an outside attorny after getting permission to take these to see if all was legit. If my buddies would of found these they would of used em for target practice or seen how far they could skip em across a pond