When I read the earlier reports, I did wonder who saw him and who reported on this. IIRC, when this first came out, there was some suggestion that one of the librarians had actually alerted LE, since Berger did this over several trips to the library. In addition, while the head librarian was replaced shortly after the whole thing came out, he seems to have cooperated at some point (after his initial response, which was to call Clinton's lawyer!).
I doubt that anybody has the fragments, though.
I bet they caught a lot of it on surveillance tape.