The authorities later said the suspect was a Norwegian national.
Hm. Up to a point, Lord Copper. 'The BBC and half the story', as the saying goes hereabouts.
The BBC knows what it's up to, and it's clearly being very deliberate in its careful obfuscation.
Later Update: In a further edit to the BBC's main article about this, the BBC has dropped the word 'extreme' from “Police said they consider the attack an act of extreme Islamist terrorism.”