More than eight months after the 9/11 anniversary attacks on the U.S. mission in Benghazi, Libya, the CIA is still trying to find out how the attack that killed two former Navy SEALs at the agency’s annex transpired.

The attack on the CIA base came more than seven hours after an armed mob stormed the U.S. diplomatic mission in Benghazi, setting the compound ablaze and killing U.S. Ambassador to Libya Chris Stevens and Sean Smith, a State Department communications officer who was with him.

On Wednesday, Deputy CIA Director Mike Morell—along with CIA officers who were at the agency’s Benghazi base on the night of the attack—testified at a classified hearing before the House Permanent Select Committee on Intelligence. In the closed hearing, according to U.S. officials with knowledge of the proceedings, Morell was asked by Republican members about how the second wave of attackers knew to go to the CIA annex, which was a mile away from the diplomatic mission. Morell responded that at this point the CIA did not know whether the attackers had known the location of the annex or learned about it on the evening of the attack, according to these sources.

The attackers fired five mortar rounds within 90 seconds at 5:15 a.m. on September 12, according to the State Department’s official review of the Benghazi incident known as the Accountability Review Board (ARB). The last three mortar rounds hit the roof of one of the CIA annex buildings, where two CIA contractors and former Navy SEALs, Tyrone Woods and Glen Doherty, were keeping watch. Both men were killed by the mortar fire; another diplomatic security officer standing watch on the roof was severely injured, nearly losing a leg.

How the attackers knew about what was supposed to be a secret CIA facility is important. If the attackers had known for weeks about the facility and had staked out a position to fire the mortar rounds, it suggests the Benghazi attack was planned in advance and not the “flash mob with guns” that Obama administration officials described to reporters in the weeks following the attack.

If the attackers learned the location of the facility that evening, it would suggest the Benghazi assault was more of a target of opportunity and was therefore not planned well in advance of the 11th anniversary of the Sept. 11, 2001, terrorist attacks on New York and Washington.

One U.S. official familiar with the briefing told The Daily Beast that one working theory about the attack on the annex is that the militants that fired the mortars learned of the CIA annex location earlier that evening, when Woods and others rescued U.S. personnel from the diplomatic mission, and then drove a convoy through Benghazi to get to the annex. The convoy carrying the Americans was chased and fired on by attackers along the route back to the annex.

However, one U.S. intelligence official with detailed knowledge of the events in Benghazi disputed that view. This official said the Special Operations team that arrived by aircraft that evening from Tripoli was tailed by the attackers on the drive from the Benghazi airport to the CIA annex.

The State Department’s own ARB says the Special Operations team from Tripoli arrived at the annex at 5 a.m. Benghazi time. “Less than 15 minutes later, the Annex came under mortar and RPG attack, with five mortar rounds impacting close together in under 90 seconds,” it says.

When asked whether the Special Operations team from Tripoli was followed from the airport to the CIA annex, Morell said he did not have any evidence to support that claim, according to U.S. officials familiar with the closed hearing.