The Somali militant group al-Shabab claimed responsibility for the attack and said it was in retaliation for Kenya's sending of troops into Somalia. The group, which is linked to al-Qaida, had threatened large-scale attacks for years, and it has said more will be carried out unless Kenya withdraws.
The mall siege was carried out by four men with AK-47 assault rifles, but the standoff turned into a four-day fiasco that saw the mall go up in flames and a section of the structure collapse. Afterward it was revealed that Kenyan army troops looted high-end merchandise inside the mall during the siege.
Remains were found in the mall's rubble that the official said are believed to be those of the attackers. The remains are being analyzed by an FBI lab. Only four attackers were seen on closed-circuit television images from the mall, despite early reports from the government of up to 15 attackers.
Kenyan officials say 67 people died in the September attack, but some two dozen people remain unaccounted for, and the official said the toll could rise as high as 94.
Despite press reports during the mall siege that the attackers had hostages and had prepositioned weapons or ammunition inside the mall, no evidence has emerged to back those claims, the official said.