Any facility secured by only lock and key is vulnerable to anyone with a pickgun or a lock pick set and a little skill anyway. Security isn't reliant on locks, it's reliant on behavior.
If you make a fake key, then you can walk in with people all around without looking suspicious. You can even act like the owner whilst in a group of non-conspirators. Even with a great picking kit, it's going to look different to anyone looking somewhat closely.
Depending on the level of physical security surrounding the lock itself, this difference could be as extreme as the difference between knowing the password and having a great rainbow table. In the former case, you can log in as the owner without arousing any suspicion. In the latter case, you have to have some time when nobody is looking (download the hashed password database).
So get a big bright "ABC Locksmithing" shirt printed up and carry a toolbox while commiting crimes. Odds are good nobody will notice you then. Or just change the lock and come back later for the theft, now that you have a key.
I remember my elementary school got robbed. We had to sit in the auditorium for a while until they led us past the crime scene into our classrooms. I still remember a forensics guy picking up one of those plastic barrel juice boxes with tweezers and thinking about how ridiculous he looked. They ended up stealing some video cameras and stuff (back in the day pricey), but the police believed they had some inside information because they seemed to know exactly where to go.
Pretty much anywhere with windows is vulnerable. Break window, reach through, unlock door. I think that's what those robbers did.
Depending on the level of physical security surrounding the lock itself, this difference could be as extreme as the difference between knowing the password and having a great rainbow table. In the former case, you can log in as the owner without arousing any suspicion. In the latter case, you have to have some time when nobody is looking (download the hashed password database).