I'm thinking it must be an inside job. They would have to be pretty professional to be able to handle that many cars all at once and to even get them off the property. Clearly they used a transporter because they weren't found broken down two miles up the road
. But the risk of pulling off a job like that is so great they no professional would want to try something that big without knowing they would be able to get away. That suggests someone on the inside who knew exactly what the vulnerabilities were and how quickly they could exploit it and get out. Maybe a disgruntled recently terminated former employee.