Tonight we are gaining new insight into what is now believed to be a meticulously planned attack at the Westgate Mall in Nairobi, Kenya.
Based on intelligence, an official tells CNN it does not appear the attackers just walked into the mall.
Instead the attackers may have had access to the mall's blueprints, detailing personnel and emergency exits.
Investigators are also looking into whether the attackers rented a store in the mall and possibly stored their weapons inside the place before the attack, which killed at least 61 people and caused the mall to partially collapse.
The FBI is in Kenya and ready to start combing through that wreckage. The agency is just awaiitng permission to go into the mall where they'll look for DNA and other forensic evidence that will eventually make its way back to America's top secret bomb lab - a facility that is expected to play a huge role in determining who was behind this attack.
Our Barbara Starr gained exclusive access to the lab and is OutFront with this report.
According to a senior Kenyan government official, a woman appears to have been involved in the attack on the upscale mall in Nairobi.
Kenyan security forces finally took control of the shopping center Tuesday and are just beginning to learn more about the attackers.
At least 67 people were killed in the rampage but Kenya's president today said his nation "bloodied but unbowed."
David McKenzie is OutFront in Nairobi..
Were Americans involved in terror?
According to the al Qaeda-linked group Al-Shabaab, the answer is yes. The Somalia-based militants say three Americans took part in the attack, but the United States government hasn't been able to confirm it.
Our Martin Savidge is Oufront in Minneapolis, where Al-Shabaab has a history of recruiting Americans.
Officials tell CNN al Qaeda-linked militants are holed up in an upscale mall in Kenya. They have slaughtered more than 60 people, wounding nearly 200 others, including Americans.
The horror began Saturday when extremists stormed the mall with guns and grenades, going store to store shooting non-Muslim men, women and children.
Kenyan authorities say they have taken control of the shopping complex, but believe there may still be several gunmen inside holding hostages.
Here is what we know:
Night fell Monday in Nairobi with no clear resolution of the standoff between Kenyan forces and terrorists at Westgate Shopping Mall.
Security forces are expected to again storm the upscale Westgate Mall in last ditch effort to take out the remaining gunmen that are believed to be in there.
It's been three days since 10 to 15 members of the al-Qaeda-linked terror group Al-Shabaab overtook the mall - killing at least 62 civilians.
More than 200 people got out alive. And according to authorities at least three of the terrorists and 10 others suspected of being involved in the attacks have been arrested.
More stories are also emerging of those who witnessed and survived the siege.
OutFront: AFP reporter Nichole Sobecki. She went inside the mall just moments after the attack happened.