As investigators sift through the rubble of the partially-collapsed Westgate Shopping Mall in Nairobi, a major new development in the aftermath of the terrorist attack has been made public. The al-Shabaab operation didn’t start at the mall on the day of the attack, but began three months earlier when the group leased a retail space in the mall as cover for their preparations. ABC News reports that Kenyan authorities are now trying to determine whether the group cached weapons in the store to serve as their armory for the attack:

The terrorists who attacked the Nairobi mall rented a shop there for three months leading up to the devastating attack that killed at least 72 people and injured hundreds more, according to the Kenyan Interior Ministry.

Authorities are also investigating whether some of the attackers had smuggled in weapons and explosives into the Westgate Mall before the attack took place this past Saturday, according to law enforcement officials.

The attackers detonated improvised explosive devices inside the mall causing severe damage and likely deaths, another law enforcement official said. They also had heavy firepower and it was likely pre-positioned within the mall, the official said.

Intelligence services from Kenya and other governments knew the mall was being scouted by the terrorists, but didn’t have specific intel on an attack:

A former diplomat who lives in Nairobi and maintains Kenyan government and international security contacts told ABC News Tuesday night that intelligence services in Kenya had detected surveillance of Westgate Mall being conducted in the past year, but said hard intelligence it was being targeted for a terror attack wasn’t uncovered.

“The intelligence hasn’t been specific,” the former diplomat told ABC News. The former diplomat described the al-Shabab attack as “strictly for revenge” because of Kenya’s help in defeating the terror group al-Shabab in Somalia. The ex-diplomat said Muslims were “executed” alongside non-Muslims in Westgate. “It was completely indiscriminate murder,” he said.

Kenya arrested 11 terrorists, which may be a big intelligence coup that pays off later.  Meanwhile, though, al-Shabaab claims to have killed 137 people in its siege of the upscale mall.  The government rejects the claim:

The militant group behind the takeover of a Nairobi mall claimed Wednesday that Kenyan government assault team carried out “a demolition” of the building, burying 137 hostages in rubble. A government spokesman denied the claim and said Kenyan forces were clearing all rooms, firing as they moved and encountering no one.

In a series of tweets from a Twitter account believed to be genuine, al-Shabab also said that “having failed to defeat the mujahideen inside the mall, the Kenyan govt disseminated chemical gases to end the siege.” It did not specify which gases, which could theoretically include anything from tear gas to poison.

Government spokesman Manoah Esipisu told The Associated Press that no chemical weapons were used, that the collapse of floors in the mall was caused by a fire set by the terrorists and that the official civilian death toll remains 61.

“Al-Shabab is known for wild allegations and there is absolutely no truth to what they’re saying,” he said. But officials said the death count will likely rise. Estimates varied between only a few bodies to dozens of bodies possibly still inside the mall.

Before the final assault, the death toll was at 62, and some estimates had another sixty bodies left to be recovered in the mall, so 137 may not be far off.  It’s unlikely that the terrorists had time to do a body count and get it back to their social-media arm in any kind of accurate manner, though.  It may take some time to go through the entirety of the rubble and identify the victims, as we found on a much larger scale on 9/11 in New York City.  Regardless of body counts, this has been a horrible failure of intelligence, but one that might provide better preparation for the next time an Islamist terror network tries a Mumbai re-run.

Update: CNN reports that Kenya is backing away from its earlier statements on the nationalities of the terrorists:

Kenya minister not yet able to confirm nationalities of terrorists until forensic tests done. http://t.co/mNq8ObKb1x

— CNN Breaking News (@cnnbrk) September 25, 2013

Mary Chastain has been howling on Twitter over the media reports on supposedly confirmed nationalities.  We know Americans are in al-Shabaab, but that doesn’t mean they took part in this attack — and in one sense, that may not make much sense if the terrorist group wants to conduct attacks here.