Norwegian man Hassan Abdi Dhuhulow has been named as a suspect behind the Westgate shopping mall attack in Nairobi, Kenya, last month.
The 23-year-old, who is of Somali origin, was named by the BBC's Newsnight as one of four men pictured in CCTV footage released by Kenyan authorities.
The Somali-born Norwegian was said by relatives to have returned to Somalia in 2009, making increasingly erratic phone calls to the family.
Six Britons were killed in the assault on the shopping centre, which lasted four days and left some 67 people dead. The al Qaeda-linked Somali Islamic extremist group al-Shabaab has claimed responsibility for the assault.
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Dhuhulow is said to have been born in Somalia but his family moved to Norway as refugees in 1999, making their home in the town of Larvik, 75 miles south of Oslo.
One relative, who spoke anonymously to the BBC, said Dhuhulow left for Somalia in 2009 and the last of his rare phone calls in the summer said he was in trouble and wanted to come home.
After being shown the CCTV film, the relative reportedly said: "I don't know what I feel or think... If it is him, he must have been brainwashed."
Former neighbour Morten Henriksen said one of the attackers on the video clip, in a black shirt or jacket, could be Dhuhulow, whom he described to the programme as "pretty extreme".
Last week, Norway's intelligence agency, the PST, said it had sent officers to Kenya to verify reports that a Norwegian citizen was involved in the attack on the Nairobi mall.
At one point Kenyan authorities said a woman might have been involved in the attack, prompting speculation that British terrorist suspect Samantha Lewthwaite - who was married to July 7 bomber Jermaine Lindsay - might have had some connection with the attack.
Dubbed the ''White Widow'', Lewthwaite is known to be in East Africa and is wanted over alleged links to a terrorist cell that planned to bomb the country's coastal resorts. Interpol issued a notice asking for help in capturing the 29-year-old fugitive over the 2011 plot.