I have attended those "abandoned/unpaid storage unit" auctions before and also watched that neat show on TV a lot which was about storage unit auctions so I got pretty familiar with how it all works.
You are correct that the owner of the storage facility will make attempts to contact a renter to give them a chance to make due on their balance before an auction is held on their unit, however, what happens sometimes is the renter moves to a different state or different house and doesnt contact the storage facility about their new address or new information , and so the storage facility a lot of times has trouble finding out how to even contact the renter on unpaid units.
So it is a pretty dicey situation really.
Every time I went to one of those auctions I always felt a little guilty bidding on other people's "stuff". Most of the time the stuff wasnt super valuable but there was that breaking news story awhile back where a buyer of an auctioned unit found millions of dollars in one (link below), so sometimes every now and then there can be real valuables in them.
Jewelry, and really nice stuff can be found sometimes in them.
We of course dont yet know the reason for these murders but I do think its possible that a renter of a storage unit may have gotten mad his stuff was sold. Someone linked back that the auction was not long ago before the murders.
That is where this theory may be more plausible because of the timing of the auctioned units being so close before the murders.
Finders keepers? Buyer finds $7.5 million in cash in auctioned Southern California storage unit