All this will do is download the public information on everyone on your friend's list (according to my reading of the code). I believe this is also against Facebook's TOS.

If you can view the Facebook profile of the blackmailer, you may also look and check the previous posts if it's shown publicly. Find any hint/clue on his comments or the comments on his posts. If he is posting a kind of stuff that is searchable that may lead to the connection.

Why not make also a dummy/fake account? Be friends to his list of friends and try to contact them, maybe you can find any related pieces of information.