The scroll and the keys remain lying where they are. The robotic cockroach should get a good image of the keys, and determine that they are all for different locks. The shape of each key, like the material used, is different.

If anybody looks close enough at the scroll, they might note that there's criss-crossing lines upon it, suggesting a map more than anything else. Unravelling it will determine the truth of the matter, anyway. Besides, there may be a name on it to see who left it behind.