Norway: Growing belief in home-grown plot
Police are being careful to avoid speculation about the motives behind the Norwegian attacks.
However they are indicating that the suspect for both the Oslo bomb and Utoeya shooting is in custody and is co-operating - and may want to explain his motives.
The strong suggestion has been that the attacks are linked to domestic rather than international terrorism with a strong political agenda.
Initially on Friday speculation centred on an al-Qaeda-linked attack - perhaps because of the presence of Norwegian troops in Afghanistan.
But the choice of targets and the revelation that the gunman was Nordic in appearance began to change that assessment as the day went on.
A domestic agenda would explain the decision to target a political youth camp rather than carry out a more straightforward mass casualty attack in the city.
There are similarities with the 1995 Oklahoma City bombing against federal buildings in the US. Then, the finger was initially pointed at international terrorism before it became clear it was home-grown.
The perpetrator of that attack, Timothy McVeigh, did have some help from other individuals and the Norwegian authorities will be wanting to establish as fast as they can if the suspect in this attack was acting alone or was part of any wider group or network in which others assisted him.
This is crucial in case they pose a danger.
Police have not ruled out the possibility that others were involved but nor have they confirmed it.
If others were not, there will be questions about how one individual was able to wreak so much devastation and how he was able to build an effective bomb - focusing, for instance, on whether he had any kind of military training.
The reality that the threat came from within Norwegian society rather than from outside will be a profound shock for a country that is used to being secure and accessible with relatively few of the security measures seen in a country like Britain.
The Norwegian prime minister has been clear that this was an attack on the country's democracy and values and once it is understood what the motives were, the question will be how the sheer scale of this atrocity affects the way in which people live in Norway and think about their society.