Some went outside, only to turn around and go back into the four-story mall after realizing bullets were flying there as well. Kaigwa-Okoye was among them, joining about 20 people who took shelter for about five hours in a women's bathroom cubicle.
"They had grenades, and it was really, really loud," he told CNN, adding that he noticed tear gas in the corridors as well. "All of us felt like they were close."
As people texted family and friends outside the mall, word spread that nobody could be trusted -- and, even if the good guys could be sorted from the bad guys, the barrage of intermittent gunfire made any escape seem futile.
Sara Head, a Washington resident, experienced similar horror in the mall's parking garage. As her car pulled up, she and others heard gunfire -- prompting them to crawl underneath and sneak behind cars before getting into a stairwell. She had company there, including two people bleeding from gunshot wounds.
Eventually, the stairwell lights went back on and the door to a nearby supermarket opened, so they dashed through and past a nearby loading dock to safety.
"There was blood throughout the supermarket," Head recalled. "... It wasn't clear if it was OK to exit. I was short of sheep following."
Soldiers crawl under cars, copters fly overhead
By then, the sight of Kenyan soldiers in military fatigues crawling under cars with their guns cocked made clear that the once shiny, pristine Westgate mall had become a war zone. The whirr of surveillance helicopters overhead drove home the point.
Police took those leaving the building in a straight line, arms raised in the air. They were all taken to a secluded place for vetting to ensure they were not attackers.
The military asked media not to televise anything live because the gunmen might be watching screens inside the mall and therefore take cues on their movement.
And everyone else, except for authorities, was urged to stay away as roads and nearby locales, including another shopping center, was closed down.
The U.N. Security Council condemned the attack "in the strongest possible terms," voicing solidarity with Kenya while calling terrorism "one of the most serious threats to international peace and security."
Most of the casualties are Kenyan, authorities said. But the mall is popular with expatriates and foreign nationals, who are among those killed and injured.
That includes two dead French nationals, their government said. Likewise, two Canadians -- one of them a diplomat -- died in the attack, according to Prime Minister Stephen Harper's office.
U.S. Secretary of State John Kerry said there were several Americans among the injured but none among the dead, though the wife of a foreign national working for the U.S. Agency for International Development was killed.
"As we prepare to bring the world's leaders at the United Nations next week," Kerry said in reference to the upcoming U.N. General Assembly, "we are reminded again in tragedy of our common humanity."