In security camera video seen by The Associated Press yesterday, some members of Kenya's armed forces appeared to loot a store during the four-day siege of Nairobi's most upscale mall.
At least 67 people were killed in the attack by Islamic extremists.
Kenya's security forces have previously denied any wrongdoing.
Soon after the attack began on Sept 21, Kenyan officials put a security cordon around the mall, allowing only security forces and a few government personnel to pass through.
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Mobile phones were ripped from displays, cash registers emptied, and even alcohol stocks plundered, according to AP reporters at the scene after the siege ended.
Public servants in Kenya, including police, firefighters and soldiers, are poorly paid and frequently accused of corruption.
An investigation into a huge fire at Nairobi's airport in August revealed that first responders had looted electronics, a bank and an ATM during and after the blaze.
In the case of the Westgate attack, a team of Kenyan lawmakers that investigated the looting allegations cleared soldiers of any wrongdoing.
Local and foreign investigators have since been digging through the rubble for evidence, and yesterday another body believed to be that of one of the mall attackers was retrieved.
Interior Minister Joseph Ole Lenku said in a statement that it was the fourth body that "we know from CCTV footage to be that of a terrorist. DNA and other investigations will confirm their identities."
Four AK-47 assault rifles believed to have been used by the attackers were also recovered, the statement said.
Many questions, including what caused a part of the mall to collapse, remain unanswered nearly a month after the attack.
Kenyan officials have urged patience, saying they need more time to investigate the scene.