This morning, the locksmith came and quickly replaced the lock. Upon closer examination in the light of day, it was obvious that in fact someone had pried my box open. Other boxes in the same pod had pry marks on them, as did the adjacent pod, which also had another box with no lock on it. We don't think anything of value or importance was taken from my mailbox, because there was mail in it when I originally noticed the broken lock.
This afternoon, the mail carrier noticed that box was repaired and delivered the accumulated mail, which I appreciate. I won't have to go the post office to collect it.
While breaking in to mailboxes is a federal offense, I don't really know what to do about it. I reported it to the complex management and to the company that manages my rental, but what are they supposed to do?