A former British citizen developed deadly chemical weapons for extremists who murdered dozens of people in the attack on the Kenyan shopping mall, it has been alleged.
Madhi Hashi, was born in Somalia, but then raised in Camden, north London from the age of six, becoming a British citizen when he turned 17.
Now aged just 24, he had his citizenship revoked by Theresa May last year, as he sits awaiting trial in New York on terror charges.
Now he is accused of being one of the masterminds behind the atrocity which left 67 people dead in the upscale Westgate mall in Nairobi - given deadly militia training by al-Qaeda linked group Al Shabab.
Hashi is accused of being a member of "an elite al-Shabab suicide bombing unit" and having "specific knowledge regarding significant al Qaida members operating in East Africa who sought to carry out attacks against US and Western interests", The Times reported.
The newspaper said that while not charged with offences relating to chemical weapons, it is alleged that Hashi and his two co-accused had "substantial knowledge" on an al-Shabab department that was developing chemical weapons and that this will form part of the case against them.
Hashi and the two other men are still awaiting trial, on charges that between 2008 and 2012, they travelled to Somalia to receive weapons and explosives training from al-Shabab and were ''deployed in combat operations'' there.
The trio were captured while preparing to travel to Yemen to allegedly meet up with al-Shabab members.
A Foreign Office spokesman said: "The FCO became aware of Hashi's detention by US authorities on terrorism-related charges in 2012."