Iran sheltered at least two of the leaders of that attack and mat still be protecting them today.
Sandy Berger, Clinton had no interest in pursuing this investigation since it led to Iran:
http://www.wsj.com/articles/SB115102702568788331
http://www.fbi.gov/news/pressrel/press-releases/terrorism-charges-have-been-brought-against-13-members-of-the-pro-iran-saudi-hizballah