What seems a little crazy to me is to take a chance breaking in with all the CCTV's these days. Also - how did the guy that broke in know you had not already removed the machines unless it was an "inside job".
Think about it - with most storage unit auctions contents need to be removed right after the auction - these guys broke in the middle of the night the following night - in most cases contents would be long gone already! Something just does not make a lot of sense here? Girl at counter might be a good place for police to start? She was really the only one who knew machines were paid for and still in that unit.
Beyond that who is going to take just two machines once they break in? If you are going to take that risk most people would have grabbed all 4.
One last thing - it had to be two or more people unless it was done with a lift gate or ramp. So why would you not load all 4 once you have a ramp out? Getting "scared off" isn't really an answer because no one would know if you owned that unit or not if they saw someone emptying it. I rent several storage units here in PA and I don't have a clue who is coming or going when I am at the storage place. I have never met more then about 5 other renters in the 10 years I have been their and I am their almost daily.