Editor's note: Paul Cruickshank and Tim Lister are writing a book about Morten Storm and his life as a former informant on terrorist groups.
(CNN) -- Western intelligence missed a chance to capture or kill the suspected terrorist thought to be behind the Nairobi mall massacre, according to a former informant for both the CIA and the Danish intelligence service.
Morten Storm, who worked as an informant for five years, had forged a close relationship with the man -- a Kenyan called Ikrima -- who has been responsible for planning attacks inside Kenya for Al-Shabaab.
Storm, a Danish national, told CNN that in March 2012 the Danish intelligence agency PET had offered him one million Danish krone ($200,000) on behalf of the CIA if he could lead them to Ikrima, the target of an unsuccessful operation by US Navy SEALs last month. The SEALs raided an Al-Shabaab compound at Barawe on the Somali coast, but Ikrima escaped.
Storm's told CNN it is possible he might have got wind of the plans had he still been working for Western intelligence. But his relationship with PET and the CIA ended in mid-2012 amid disagreement about a different mission in Yemen.
"I get really frustrated to know that Ikrima had been maybe involved in the Westgate terrorist attack. It frustrates me a lot because it could have been stopped and I'm sad I can't be involved in this."
The CIA refused to comment on Storm's claims; a spokesperson for the PET told CNN: "We can't confirm or deny ever knowing Morten Storm."
Kenyan counter-terrorism sources have told CNN they believe Ikrima had a hand in the Westgate attack as well as a string of plots targeting Kenya in the last two years, including a plot to target Kenya's parliament in late 2011.
Storm said he first put Ikrima on the radar screen of Western intelligence in 2008 when he met him in Nairobi for the first time. In the spring of 2009 Storm met Ikrima in Nairobi again. Abdelkadir Warsame, a senior Al-Shabaab operative, had sent Ikrima to meet Storm to pick up electronic equipment for one of Al-Shabaab's leaders. What Ikrima did not know was that Storm was working for PET, MI6, and the CIA, and that tracking devices had been hidden in the equipment, which included a laptop.
The equipment, according to Storm's Al-Shabaab handlers, was for Saleh al Nabhan, one of the senior planners of the 1998 bombing of the U.S. embassy in Nairobi. Several months later Nabhan was targeted and killed in a U.S. Navy SEALs operation. Storm's Al-Shabaab contacts subsequently told him they believed Nabhan had been tracked through the electronic equipment but blamed a junior courier.
After Al-Shabaab carried out a twin suicide bombing attack in Kampala, Uganda in July 2010 Ikrima told Storm it was now difficult for him to travel to meet him in Nairobi. From then on the two kept in frequent touch through encrypted emails -- which CNN has seen -- providing Western intelligence with real-time information on his movements and plans.
In early 2010 Storm connected Ikrima to Anwar al Awlaki, the American-Yemeni cleric who had by then begun overseeing al Qaeda in the Arabian Peninsula's operations against the West. According to Storm the two then began communicating over encrypted emails. They eventually came up with a joint plan of action to attack the West: Ikrima would send Shabaab recruits, including Westerners, to Yemen for terrorist training, and they would then be sent back to Somalia or on to the West.
"And as for going to hooks [Awlaki's] place ... then i was told by hook that they want to train brothers and then send them back or to the west," Ikrima wrote to Storm in November 2010.
Storm believes Ikrima's connection to Awlaki -- and his delivery of equipment secretly supplied by Western intelligence - enabled Ikrima to quickly climb Al-Shabaab's hierarchy.
"He was one of the smartest ones I met in east Africa," he told CNN.
Storm told CNN that Ikrima helped oversee an intelligence apparatus -- "Amniyat" - Al-Shabaab set up in Kenya. "He's the main link between Somalia and the Al Hijra group back here in Kenya," one of Ikrima's former associates told CNN in Nairobi. Al Hijra is a militant outfit in Kenya closely associated with Al-Shabaab.
Storm said that Ikrima was at the center of a spiderweb connecting terrorist operatives in Somalia, Kenya, Yemen, and the West. He said he had emerged as the chief handler of foreign fighters, including Westerners joining Al-Shabaab, placing him in a unique opportunity to plot terrorist attacks in East Africa and Europe.
His intelligence, language skills and connections appear to have now made Ikrima invaluable to Al-Shabaab. Two former friends of Ikrima -- including a former member of Al-Shabaab, told CNN he was now a strategist and planner for the group, rather than a fighter.
"He's part of the intelligence team. He speaks five languages - Norwegian, Swahili, Arabic, Somali, and English - and that puts him in a front seat with Al-Shabaab," one of his associates told CNN.
Storm and the two former associates have shed light on how a middle class Kenyan became one of the most wanted terrorists in east Africa.
Ikrima, now believed to be in his late twenties, was born in Mombasa into a middle class ethnic Somali family who also had blood links to the Al-Ansi tribe in Yemen, a connection which later helped Ikrima forge a relationship with AQAP.
The family moved to Nairobi when he was young where he excelled in his studies, especially in French and other languages. His friends remembered him as not particularly religious and fond of smoking marijuana.
He moved to Norway in 2004 apparently to seek out economic opportunities in Europe, taking advantage of the fact that his Somali ethnicity allowed him to apply for refugee status. He was granted temporary travel papers, but he never fit in, and started to become radicalized. A 2006 offensive by Ethiopian troops to rid Somalia of the Islamic Courts Union, an Islamist militia that had taken control of much of the country, appears to have played a significant role.
Storm said Ikrima had told him he had joined the Islamic Courts Union in Somalia and experienced the invasion by Ethiopian troops first hand. He suspects the experience instilled in Ikrima a deep commitment to Jihad. According to his friends when he returned to Norway he was told his application for asylum had been rejected, and he moved to London for several months. In 2008 Ikrima left Europe for good and returned to east Africa.
Western counter-terorrism officials fear his reputation in Jihadist circles worldwide will be bolstered by his escape from the U.S. operation, and he may be emboldened to plot new attacks.
" Al-Shabaab will protect him to the end. They will give him bodyguards around the clock they will make sure he is safe where ever he goes in Somalia," one of the former associates of Ikrima told CNN.