It has taken two years but Norwegian security services have finally confirmed a Norwegian man of Somali descent was one of the terrorists who attacked a Kenyan shopping mall in 2013.

On 21 September 2013, a group of terrorists attacked the Westgate Mall, an upmarket shopping centre in an affluent part of Nairobi, Kenya. During the ensuing siege the four young gunmen, also armed with grenades, shot indiscriminately at shoppers, staff and security services killing at least 67.

It took four days for Kenyan security services to lift the siege. The Islamists were killed by a combination of police action and the collapse of areas of the mall. The Somali terror group Al-Shabaab claimed responsibility.

Ever since the events in September 2013 the identity of one of the gunmen was suspected to be a Norwegian citizen called Hassan Dhuhulow, reports Norwegian newspaper Aftenposten. 23 years old at the time of his death, Dhuhulow arrived in Norway aged nine in 1999.

Before the attack Dhuhulow was already known to the Norwegian Police Security Service (PST). Several years earlier the PST had been tipped off about him and tried to stop his radicalisation.

Although the Norwegian authorities concluded their investigation a year ago, only now has the FBI finished its analysis of Dhuhulow’s dental records. From material gathered at the Westgate Mall his identity has now been confirmed.

Matters would have been faster had the PST and FBI been able to rely on DNA data, however that was not possible in this case because of confusion about his family background.

Chillingly, given the volume of migrants currently being processed across Europe, Aftenposten reports the investigation showed the family relationships given to Norwegian immigration authorities when Dhuhulow came to Norway in 1999, were incorrect.

The woman claiming to be Dhuhulow’s sister was no relation to him and she has been charged with perjury. Convicted at first instance, the ‘sister’ won on appeal. However, the case is now to be heard in Norway’s Supreme Court.

Two other Norwegian terrorists are known to have killed overseas. A 31-year-old Norwegian Tunisian, Jamel Mahmoudi, killed eight in a suicide bomb attack for Islamic State in Baghdad last year and 44-year-old Norwegian Somali, Burhan Ahmed Abdule, killed 27 in a suicide bombing of a Somali hotel in March 2014.