Sun Jan 31, 2021 8:43 pm by malfunctionjunction
I don't know what you've got going on exactly, but about 20 years ago, I met a friend of a friend who knew just a couple things about locks. He had a follower and a pinning kit for rekeying locks as a handyman. Anyway, he had figured out the master key to his apartment building (Weiser) by taking his own lock apart and measuring the pins so that he knew which depths didn't match his own key. All he did after that was had a locksmith cut the key by code. Now days there are places online that will cut keys by code, saving them a trip to their local locksmith if they're feeling shy.
Not sure how you know it was master keys vs. picking or bumping or anything else, but I guess my point is that unless we're talking something relatively difficult, like even Best or Medeco, there are a lot of different ways for relatively unskilled people to open/bypass a lock or obtain a working master key without having access to an existing master key. (Though having access to such a key through borrowing or accessing a lock box of some sort is certainly another common method.) At the end of the day, most locks are only there to keep the honest people honest and most criminals are simply going to kick/pry/smash/cut their way into almost anything they think they want to get into.