I'd like to find this person and call the cops on them with concrete evidence.
The best I could think of is leaving fake packages outside with high resolution trackers in them. However, is there a high enough resolution tracker that can display on the map where the object has been? I know the Tile has 400ft tracking but as far as I can tell it only emits sound, not show on a map where it was last... at least not in the resolution needed in an apartment
When I had a situation where I had trouble getting packages I got a mailbox-etc mailbox where the package were dropped off at the store and I could pick them up (now the UPS Store).
There is a youtube series were someone leaves fake packages with fart spray and multiple cell phones to track the packages. They're using cell phones gps to track down the packages.
These people can be dangerous (one package seems to be destroyed by gun shots...) so I'm not sure confronting them on your own is a great idea. https://www.youtube.com/embed/h4T_LlK1VE4?start=968