I put the text of the BBC's live updates pages for the 22 and 23 July into Wordle and it created these two images for me.
The BBC began reporting that an explosion had occurred in Oslo on their live updates page at 15h30 (UK time) and initial news coverage focussed on the blast.
The shootings on Utoeya were first reported by the BBC 17h19. As events at Utoeya were unfolding during the evening, there was still plenty of Oslo-based reaction to report and details of what was happening on the island remained sketchy.
As the scale of the tragedy at the youth camp emerged overnight, the focus on 23 July shifted towards Utoeya. In the Wordle for 23 July, "Oslo" and "Utoeya" have similar weights.
Second, the Wordle shows the emergence of suspect Anders Behring Breivik on 23 July, the man arrested on Utoeya and who later admitted responsibility for the attacks.
Third, there was much more use of the word "Norway" on 23 July. In part, this may have been due to an increase in the number of general reactions published by the BBC to the attacks in the aftermath when there was less breaking news to report.