Sorry about your misfortune.
They get their values from Meth. There are clandestine labs up the road.

Also, I've seen the old "bottle from a moving vehicle" routine up there, usually drunk teens "having fun". I guess you could park off the BD-Enumclaw road and take my secret trail to the creek from the opposite bank; it's just as far of a walk, but hairy (stickers, a small cliff, log walk/balance beam, mosquitoes) I haven't cleared the trail in a couple years and have been going in from the hatchery access , when I do go.
I actually quit going there because I keep seeing window glass on the ground.
Perhaps we could stake the area out, or ask the KCSO to cruise by more often... Like that's gonna happen!
Again, sorry to hear of your misfortune. I hope the perps. get their just reward- a hammer to the forehead!