That was gonna be my qn too as it's kinda on "common property" down there, although on a techincality, it may be considered your property being the apartments storage area.
Being out of sight, there's a fair chance the thief MAY be an associate of resident in your block.
There was a burgular in the apartments next to my work last week.
Followed a car in through rolladoor, disarmed door panel so he didn't get locked in, sprayed paint over camera lenses & broke into the cars in the underground car park.