WASHINGTON—The Justice Department has filed sealed criminal charges against a number of suspects in the attack on the U.S. consulate in Benghazi that killed the U.S. ambassador to Libya and three other Americans, according to people familiar with the matter.

One of those charged, according to these people, is Ahmed Abu Khattalah, founder of Libya's Islamist militia Ansar al-Sharia. Mr. Abu Khattalah was seen at the compound when it was overrun, according to intelligence officials. In interviews with reporters, Mr. Abu Khattalah...