[bluGill]

> Yet the thieves can still somehow trade the metals.

It isn't hard to melt down the metals and extract the valuable ones. A proper factory can do a much better job (get more of the valuable metals out), but it is something I could profitably do in my backyard over a fire. I haven't looked into the details of refining platinum, but I doubt is is much different from any other metal. (when I looked into it I lived in an area with a lot of iron deposits, I've since moved and no longer have access to iron ore so that potential hobby is dead to me)

Once you have raw metals you can claim any source you want. Just form them into a ring and say you were saving it for your anniversary, but your wife left you - I'm sure you can come up with other ways to make it look like got a legal source.