Washington (CNN) - A Republican lawmaker demanded Wednesday to know why investigators have not captured or killed any of the suspects in the attack on the U.S. diplomatic mission in Benghazi, pointing out that CNN was able to find a man who some say was the ringleader in the assault that left the ambassador and three other Americans dead.

Eight GOP lawmakers are asking that incoming FBI Director James Comey brief Congress within 30 days about the investigation. They say the administration's inquiry into the September 11, 2011, attacks in Libya has been "simply unacceptable," according to a draft letter obtained by CNN.