NAIROBI, Kenya — Closed circuit television footage from a Nairobi mall attacked by terrorists last month shows four men carrying automatic weapons, a top government official said Wednesday, an indication there may not have been as many attackers as government officials first said.

Kenya's government initially said 10 to 15 attackers were involved in the Sept. 21 attack on Westgate Mall, an assault that killed at least 67 people and which the al-Qaida-linked Somali militant group al-Shabab has claimed responsibility for.

The mall security footage shows armed men casually strolling through the mall, shooting unarmed civilians. The footage may not show all of the assailants that took part in the attack, though the government official said he believes only four took part in the protracted siege. The official insisted on anonymity to discuss information not publicly released.

Six security officers — three military and three police officers — died in the confrontation, according to government officials.

Dozens of youths have been detained in the Majengo slum area of Nairobi in recent days in police efforts to track down the mall attackers.

Pathologists on Wednesday conducted autopsies on two bodies of military men retrieved from the rubble in the Westgate Mall on Tuesday.

It is not clear if the two bodies increase the death toll. A military spokesman's phone was off and could not be reached for comment.

Al-Shabab has said it carried out the attack in retaliation for Kenya sending troops into Somalia nearly two years ago. The group has promised more attacks inside Kenya unless those troops are withdrawn. Kenyan President Uhuru Kenyatta has vowed to continue the military mission inside Somalia despite the mall attack.

Kenyatta on Tuesday ordered a commission of inquiry into the attack. FBI and British forensic experts are at the mall working alongside Kenyan investigators to find any remaining victims and piece together what happened during the attack and four-day military siege that followed.