Though native to the Bone Forest, they have been seen all over as they follow those with riches and good food. The thing that makes these squirrels so interesting is their seemingly extra-dexterous hands that can both pick locks and unfasten clasps alike with great ease. Though most of the time the squirrels take only a little to avoid being noticed, a much larger pack was reported to have taken everything off of a 7 cart caravan that was transfering a large shipment of both assorted foods and fine jewelery. Though they have no use seemingly for the jewelry other than lining their nests, they take it none the less out of habit of the master that trained them. Originally just black squirrels, Billy Trull found, trained, and bred the most inteligent and dexterous ones and he came with what would eventually be called "the robber squirrels". Though they have gone by other names and their deeds are often mistaken as omens of either haunting or angry forest spirits, they have no knowledge or care of things destroying the forest as they can survive fine in the city just as well as they do in the forest.
Billy Trull, a rogue of great note, was born in the City of Two Halves to a poor prostitute and a thankless john. Having been born into the slums of the city he had grown up wishing for better. As he grew older he found he had a knack for training animals and stealing things, and when he decided to strike it out he achieved a great many things, one of his lesser known achievements was one of the most annoying breeds of squirrels known to man.
Encountering the Beast
When the PCs first encounter the squirrels they will notice, if they do well enough, that all the squirrels in this area are black and have little white crests on their chests, and while they look to be the size of ordinary squirrels they travel in small packs of 5 to 7. Whether these are being controlled by a greater force, such as a small band of bandits, or working for the purpose Billy created them for, to provide for the needy.
Sorry this is a bit short :/ still I look forward to your comments and criticism
Additional Ideas (1)
Because they have no master to take it to, and after they kept the soft things for their lair, the rest is strewn randomly throughout the forest, dropped whenever they get tired of carrying it or when it falls out of their mouth/paws.
Many children (and even more adults) have gotten very lucky finding jewelry walking through the woods so it has become a popular past-time of the locals. Whenever they hear of a new robbery, most of the locals sneak out into the woods to do a walking search. Few, if any, would ever tell those that were robbed about the situation.