U.S. Ambassador to Libya Chris Stevens and three of his staff members died after the U.S. consulate in Benghazi was overrun Sept. 11, 2012.
The FBI published grainy images of three individuals it says were on the grounds of the consulate at the time of the attack.
"The FBI is now asking Libyans and people around the world for additional information related to the attacks," the agency said in a statement. "These individuals may be able to provide information to help in the investigation."
U.S. lawmakers are searching for answers regarding the attack. Members of the House of Representatives questioned U.S. Secretary of State John Kerry recently on what sort of security was in place at the time of the attack. Hillary Clinton faced a similar line of questioning before she stepped down as secretary of State.
The U.S. State Department warned in March that the security situation in Libya was "unpredictable." The French Embassy in Tripoli was attacked last month.
The U.S. government described the Benghazi incident last year as an act of terrorism.