As few as four to six militants are now expected to be behind Kenya’s Westgate mall attack that left upwards of 60 civilians dead. According to the New York Times, a sluggish investigation is underway and still the number and names of rebels is up in the air.

Despite gathering information from security cameras and witness accounts, the report said, only “noms de guerre” or code names could be identified. The report noted that 10 to 15 armed Al-Shabaab militants were originally said to be responsible for the attack.

Serving as an Al-Shabaab and Somalia expert at Washington D.C.’s Foundation for Defense of Democracies, Daveed Gartenstein-Ross told the New York Times plainly:

“For Kenya, there’s still not a lot of clarity about the specifics of the attack.”

“It’s been obvious over the course of this year that they’ve been involved in increasingly sophisticated attacks, Daveed Gartenstein-Ross continued. “They’ve clearly shown the ability to project power into Kenya.”

According to The New York Times, Al-Shabaab’s ability and reasoning behind extending targets to networks in Africa stems from a 2010 declaration of adherence to Al Qaeda, founded by Osama bin Laden.

“There has to have been a significant period of surveillance and planning and effort to prepare for this,” an anonymous official said in the report. “They were too well organized. They were too clear about where they were going and what was happening for there to have been anything but a period of surveillance and a good understanding of what they were going to do.”

Bodies that have recently been recovered from the September 21 attack have not been distinguished as the corpse of a victim or militant, although the report said that rebels executed victims who were wounded.