Large academic libraries might have theses and dissertations but, again, they won't circulate but can be read or copied (paper trail?).
No, the interesting stuff isn't available, Hillie master's thesis and Traitor John's military records, the Congressional Record prior to 1984 or the New York Times online prior to 2001. No, there is more interesting stuff on Cryptome than in my library!
The only thing I can figure is if somebody is looking into building histories, blueprints, photos, layouts and infrastructure-like things that could lead someone to help in planning a terrorist act. That kind of public-records stuff might be more readily available in a library than on the internet.
Most libraries have Internet terminals so people can access the Web that otherwise couldn't.
So terrorists can use these terminals for terrorist communications without fear of being monitored. It isn't a trivial thing really.
Aren't there bomb making books in most libraries.....me thinks that's what they'd be reviewing....especially, if it's some Islamic under surveillance.....