yeah, they had to be tipped off somehow. On today's market that could be 5 or 6 grand of stuff, I'm guessing it was stolen and the fools that stole it didn't know what to do with just the uppers, figured it was better to dump them.
+1 on that.
Criminals/low-lifes dealing in stolen property with no idea what to do without lowers. And maybe they found out after a little amatuer research that the lowers have to be FFL'ed, NICS'ed, and are the serialed/traced part. (and that AR lowers/LPK's are also still somewhat inflated in price and hard to come by in the Obama market right now...)
And the .223/5.56 'boolits'/caps did not fit any of their other 'gats', so dumped it all. Someone else saw it in the dumpster and called it in.
To us in the "gun culture" trying to think of how to profit from such loot realize that we could have sold it all at a gun show for cash, probably within less than an hour, and not even been in violation of any laws, other than dealing in presumably stolen property, that is. Or if we wanted to be careful, could concoct a cover story about them being our "dead father's gun stuff" etc. and sell them quietly one at a time every few weeks etc.
The one thing that we here reading this story and being confused is that we keep trying to apply
rational non-criminal logic to their actions. I suspect anyone with a LE background will tell you to chuck that line of reasoning out the window. Criminals (at least low-level property crime) are by definition opportunistic and lazy. Also, if they had better intelligence or mental faculties, they'd find better prospects in the law-abiding world, or at least move into an organizing or king-pin type of role within the criminal arena.