The report, made public Tuesday, discredited assertions made by Kenyan authorities claiming as many as 15 attackers were involved, possibly foreign nationals, and no hostages were held, NBC News reported.
More than 60 civilians and six soldiers died in the siege that began Sept. 21 at the upscale Westgate Mall in Nairobi by terrorists from al-Qaida-linked al-Shabaab. After a 2-day siege and a series of explosions, Kenyan authorities said they cleared the mall and killed four attackers.
During a news conference in New York Tuesday, New York Police Commissioner Ray Kelly said investigators didn't know "with certainty" how many people were involved, "but we believe there were only four shooters."
The report also said the attackers carried only light weapons, and nothing indicated any of them tried to take hostages or remained in the mall after 12:15 a.m. Sept. 22, NBC News said. It said the female British jihadist known as the "White Widow" likely wasn't in the mall, despite published reports she was, and the Kenyan military looted the high-end shopping complex.
Lt. Detective Cmdr. Kevin Yorke, who prepared and presented the report, also raised questions about Kenyan authorities' theory that the attackers died when portions of the mall collapsed in bomb blasts.
"As a cop, I'm very skeptical of claims until I see proof," said Yorke, adding there is "a lot of doubt in my mind it is true."
The New York Police Department sent several detectives to Nairobi with the New York Joint Terrorism Task Force to investigate the assault.
The report said the attackers had grenades and hundreds of bullets in eight magazines, but had no body armor, handguns or heavy weapons, NBC News said. They didn't try to take hostages, but killed as many people as they could. The attackers let live some who could recite Muslim prayers or name the mother of the Prophet Mohammed.
The report credited private security guards and personnel with helping many people escape although some may have fired on each other since they didn't have badges, NBC News said. Some civilians "played dead" as the terrorists walked by, the report said.