Crucial question: Is he sane or not?

The man who carried out bomb and gun attacks in Norway last year, which left 77 people dead, has pleaded not guilty at the start of his trial in Oslo.

Anders Behring Breivik attacked a youth camp organised by the governing Labour party on the island of Utoeya, after setting off a car bomb in the capital.

If the court declares Breivik criminally insane, he will be committed to psychiatric care.

If he is judged to be mentally stable, he will go to prison.

Professor Jo Stigen from the University of Oslo told the BBC the judge will have to decide what his state of mind is.