U.S. intelligence and counterterrorism officials are testifying before Congress about the deadly September attack on the U.S. consulate in Benghazi, Libya.

The House and Senate Intelligence Committees began closed-door hearings Thursday on the attack in which U.S. Ambassador Christopher Stevens and three other Americans were killed.

Many lawmakers are concerned over whether there was adequate security at the consulate, and if the Obama administration later attempted to hide information to avoid any embarrassment before the November 6 presidential election.

Former CIA director David Petraeus is among those scheduled to appear before the House committee Friday. Petraeus resigned last week following an FBI investigation that uncovered his extramarital affair with his biographer, Paula Broadwell.

Attorney General Eric Holder said Thursday that he felt “very secure” that there was no breach of national security in the Petraeus scandal. Holder said that if the investigation uncovered any security threat, he would have informed the president and Congress.

In another development, House Foreign Affairs Committee chairwoman Ileana Ros-Lehtinen said Secretary of State Hillary Clinton will testify before a committee next month.