The owner later learned the thefts — at least six so far — could be the work of an entire ring of furry thieves, or at least two critters. “A black one (or more) and a light brown/grey one (or more),” the owner wrote.
Looks like the owner is dealing with a MULTI-NATIONAL SQUIRREL CRIME RING.
Years ago I had a bird feeder. Squirrels took it over and kept the birds away. I noted that we had birds of prey in the area. So I moved my bird feeder into a wide open area and loaded it with corn. The hawks thanked me. There would be squirrel tracks in the snow that ended abruptly where a swooping bird of prey caught the little thieves.