Ali Salim Gichunge, the key suspect in the DusitD2 attack, was a feared militant working for Al-Shabaab’s Amniat squad.
Amniat is the group’s internal team that grills fighters to smoke out possible sympathisers or spies.
A former Al-Shabaab fighter said he met Gichunge alias Farouk in Somalia back in 2012.
Gichunge is believed to have been felled by commandos who responded to the attack at the swanky hotel.
The ex-fighter said Gichunge grilled him over lunch in efforts to gauge his commitment to war.
"They'll eat with you but they are just interrogating you: 'How do you love Al-Shabaab? How did you come here? Why did you join Al-Shabaab?' That sort of questions, but we knew he's interrogating us," the reformed fighter told CNN.
CNN has concealed the reformed youth obviously for his security.
He told the international outlet that he recognized Gichunge the minute a screen grab of a CCTV footage of the gunmen entering DusitD2 surfaced online.
"I was shocked. When I saw the CCTV I said 'I know that guy! The source added.
CNN said they had carefully analysed the source’s account of things and verified that he was indeed an Al-Shabaab fighter.
“… video evidence he had of his time in Al-Shabaab, were examined by CNN and proved beyond doubt that his claims to have been a fighter in Somalia were legitimate,” CNN said