Relative says 23-year-old left Larvik for Somalia in 2009 and told his family in his last phone call home that he was in trouble

A 23-year-old Norwegian citizen of Somali origin has been named by the BBC as one of the suspects in last month’s attack on Kenya’s Westgate shopping centre.

The man, who reportedly arrived in Norway with his family as a refugee in 1999, is said to be one of four men seen in CCTV footage released by Kenyan authorities.

At least 67 people died in the Nairobi attack for which the al-Qaida-linked group al-Shabaab claimed responsibility.

The BBC’s Newsnight programme on Thursday said it had spoken to a relative of the Norwegian man, who said the man had left the town of Larvik for Somalia in 2009. The relative, who spoke to the programme on condition of anonymity, said the 23-year-old had made infrequent but increasingly erratic phone calls to the family. The most recent had been in the summer when he said he was in trouble and wanted to return home.

On being shown the CCTV footage, the relative told Newsnight: “I don’t know what I feel or think … If it is him, he must have been brainwashed.”

The programme said a former neighbour of the family in Larvik said the man had been “pretty extreme, didn’t like life in Norway … got into trouble, fights, his father was worried”. He said one person seen in the CCTV footage wearing a black shirt or jacket could be the man he had known.

Stig Hansen, an expert on security and political Islam based in Norway, told Newsnight that an estimated 20-30 Norwegians had gone to Somalia to sign up for al-Shabaab.

“The biggest problem is the so-called Generation 1.5, those who weren’t born in Norway but came when they were quite young, falling between two cultures,” he said. “[Al-Shabaab] need people who are quite ignorant about Somalia. That is in their interest because that will give them a more internationalist agenda. And it might also make them more dangerous when they return back to their home countries.”

Last week Norway’s intelligence agency, the PST, said it was attempting to verify reports that a Norwegian citizen had been involved in the assault on the shopping centre, which lasted four days.

“We have lately seen an increase in the number of persons leaving Norway to take part in acts of war, attend training camps or join terrorist networks abroad,” the Norwegian authorities said. “We are concerned that this development may have an increasingly negative impact on the threat situation in Norway.”

A Kenyan al-Shabaab leader whom US commandos targeted in a raid in Somalia on 5 October, but failed to capture, reportedly may have spent time in Norway, according to the Norwegian station TV2. It said Abdukadir Mohamed Abdukadir, also known as Ikrima, had travelled to Norway and applied for asylum in 2004 but left in 2008 before receiving a decision on his application. Norwegian officials have not commented on the claims.