The witness told how the gunman changed his clothes and mingled with other victims before he vanished in the crowd outside the mall.
“The man is of Arab origin, he changed his clothes on first floor and left with the victims as they were being rescued,” he said.
“When I saw him outside the building I told the police this is one of the gunmen but they did not heed to my plea but asked me to get out.”
The account raised fears most of the attackers may have escaped during the confusion, although some were detained or killed during the mayhem.
One of the gunmen who had earlier been detained in hospital succumbed to his bullet wounds.
Somalia’s Al-Qaeda-linked Shabaab rebels claimed responsibility for the attack saying on Twitter it was in retaliation for Kenya’s military intervention in Somalia.
“The Mujahideen entered #Westgate Mall today at around noon and are still inside the mall, fighting the #Kenyan Kuffar (infidels) inside their own turf,” the Islamist militants tweeted.
“What Kenyans are witnessing at #Westgate is retributive justice for crimes committed by their military,” the group said.
Masked gunmen stormed the teeming upmarket mall in Nairobi on Saturday, sprayed gunfire and killing around 30 people and injuring more than 60 others before holing themselves up in the complex with hostages.
The gunmen are said to have spoken in a foreign language, possibly Arabic or Somali.
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