The team of FBI agents assigned to investigate the deaths of four Americans in Libya has not been able to get into the country because of the volatile situation there, according to law enforcement officials.

U.S. Ambassador J. Christopher Stevens and three other Americans died Tuesday night when militants overran the U.S. Consulate in the Libyan city of Benghazi. The inability of FBI investigators to get to the scene and secure vital forensic evidence and interview witnesses means that the task of identifying and prosecuting the assailants will be much harder, according to former and current FBI agents.