So there is no info or post-it notes on any of the record sleeves that indicate the original owner? No markings or perhaps labels indicating where the records were purchased?
I'm guessing maybe the police didn't want to deal with storing all these boxes, taking up space while waiting for someone to claim them.
(author) I think your guess is probably correct. So far I haven't found any traceable ownership markers, but if I do, I will make an effort to return them. I suspect that the records may have been stolen from multiple sources given the high variation in preservation. I also feel it's probable they've been stolen for some time now because of how poorly they appear to have been treated — disintegrating covers, melted records, cracks, etc.
I'm guessing maybe the police didn't want to deal with storing all these boxes, taking up space while waiting for someone to claim them.