He's being identified as a 'Navy contractor'. They're not saying what kind of contractor. Could be janitorial for all we know but it likely got him into the bldg often enough to develop grudges against specific individuals, learn his way around, swipe someone else's ID, and formulate a plan.
Navy contractor at Naval Air Station Fort Worth Joint Reserve Base.
I read somewhere else that he had just started to work there, so he probably didn’t know anyone very well. And certainly not the higher ups.
In any case, he had to steal an ID to get in, so while he may have worked for them in some capacity, it doesn’t sound as if he was permitted free range of the yard.