He had worked for other intel contractors prior to that, quite possibly in exactly the same job.
This is one curious bit of the story that I am surprised other journalists haven't yet harped on Greenwald to reveal.
For instance, did GG know if Snowden planned to take the BAH job for the purposes of taking documents?
Is it known that the source of the docs is exclusively from BAH? I'm not convinced you can get such attention from a high profile journalist simply by claiming that you have Top Secret access and that you plan to leak some documents to him.
What high-profile journalist would ignore a chance to look at or publish Top Secret documents?
Call one on the phone and ask him to meet you in Hong Kong.