Some details on the preparation of the attack:
Attack in Kenya was rehearsed, U.S. officials say

The plot to attack an upscale mall in Nairobi was hatched weeks or months ago on Somali soil by the militant Islamist group al-Shabab, and a team of English-speaking foreign fighters was carefully selected, the New York Times reported Tuesday, citing unnamed U.S. officials.

The blueprints of the Westgate mall were studied, down to the ventilation ducts. The attack was rehearsed and the team dispatched, slipping undetected through Kenya's porous borders, often patrolled by underpaid — and deeply corrupt — border guards, according to the officials.

A day or two before Saturday's attack, powerful belt-fed machine guns were secretly stashed in a shop in the mall with the help of a colluding employee, the officials said. At least one militant had packed a change of clothes so he could slip out with fleeing civilians after the killings were done.
http://www.tampabay.com/news/world/a...ls-say/2143787