By Barbara Starr
U.S. security and law enforcement personnel are pressing for access to a Kenyan shopping mall where a terror attack and subsequent armed standoff killed at least 67 people.
A U.S. official with direct knowledge of the situation and the latest security assessment said authorities want to know whether any Americans were among the attackers in Nairobi as claimed by the Somali-based al-Shabaab terror group said to be behind the Westgate Mall attack.
“That is the million dollar question,” the official said. “We do not have much fidelity on this. We haven’t had access to the scene.”
Kenyan authorities have said the attackers were from a number of countries, but have not confirmed that any Americans were involved.
United States knows so far that the attack that began on Saturday was carefully planned.
“This is not something where the attackers walked into the mall all of the sudden,” the official said.
The United States is looking at the possibility the attackers stored their weapons inside the mall ahead of time, and may have rented a store in the upscale mall as a base of operations.
The United States also is looking at reports the attackers may have had access to blueprints and knowledge of where employee and service personnel stairways were located, as well as ventilation systems.
FBI experts are assisting the Kenyans on a preliminary basis. They have specific expertise in analyzing explosives and fingerprints.
But the United States wants autopsy and forensic data, including DNA samples, to help determine if Americans were part of it, the official said.
The United States also will scour any communications or intercepts for clues, according to other officials.
The official emphasized reports of Twitter accounts and “fragmentary” statements from Kenyan officials about the involvement of Americans “are not enough for us” to base a conclusion.
U.S. experts also will try to analyze any evidence of grenades and belt-fed machines guns, the official said. He noted grenade attacks by al-Shabaab are fairly common.
The U.S. belief so far is that this attack was ordered by al-Shabaab hardline leader Ahmed Abdi Godane.
“Nothing like this would have gotten off the ground without him. It’s safe to assume this is something he would have blessed,” the official said.
While al-Shabaab has used fighters in Kenya for some time, the United States is also looking at the possibility the attack involved some who crossed from Somalia into Kenya.
But the official cautioned it was premature to draw conclusions about whether al-Shabaab now poses a growing threat.
While the attack was successful, he noted that it had lost “half their safe haven” inside Somalia. Al-Shabaab has also lost control over the southern port of Kismayo, which funded much of its operations in the past.
However, there are a growing number of fighters across East Africa who are now seen as loyal to the group, believing that Somalia is still lawless enough for them to operate.
"Despite being severely weakened as an insurgency, al-Shabaab’s lethality as a terrorist outfit has been fairly constant," another U.S. official said. "Al Shabaab’s operational arm may be benefiting from additional resources now that the group is less preoccupied with governance.
“The assault on the Westgate Mall in Kenya was the most prominent in a string of terrorist attacks in Somalia and Kenya stretching back over the past two years. It’s really too early to say if al-Shabaab’s latest attack is the beginning of a broader campaign in Kenya or a desperate attempt to compel Nairobi to withdraw its troops from Somalia,” that official said.
The first official pointed out as well planned-and large-scale– as the attack appears to have been, so far it seems to have been a fairly typical of Al Shabaab capabilities using conventional hand-held weapons.
One question is whether the attackers had safe houses in Kenya before and after the assault.
While the United States believes al-Shabaab was behind the attack, the incident also refocuses attention on a continuing al Qaeda cell in East Africa that has existed since the 1998 attack on the U.S. embassies in Kenya and Tanzania, the first official said.
While many of those militants have been killed or jailed, the United States has been tracking second and third generation fighters from the original group.
The United States additionally wants to know if they had any involvement, given statements by Kenyan authorities that the attack was an al Qaeda operation.
That al Qaeda group closely cooperated with al-Shabaab in the 2006 to 2009 timeframe. While they fell out after that, there is concern they might have regrouped.
CNN's Evan Perez contributed to this report.