I think that it is one of your neighbours Marie and the
manager doesn't know how to handle it, she won't tell
you who it is, ever, because she has had to pass it to the
company head office, they don't want neighbours fighting
in the stairs!
The fact that billions of packages stolen proves that the vast majority of people are decent, ethical people. But there are some, who aren't. You don't build a roof for sunny days, but for the rainy days.
I did talk with the manager and said she is going to reinforce with whomever that deliveries must be made directly to the tenant apartment. Technically. the table for packages is only for the US Postal Service to place packages too big for our mail box
My Amazon box clearly stated it was headphones. Delivery guy took pic and I showed up an hour later, package gone from vestibule of condo bldg. 99% sure the hired-for-xmas driver took it after taking pic.
Called Amazon, they agreed and sent new.