Honor killing in Norway?

As usual with Aftenposten, at least the English language version, details are sketchy. But it appears that a 30 year old man shot to death his three sisters:

The three sisters, aged 13, 24 and 27, lived in the flat in Oslo's Kalbakken district with their three brothers, their wives and children. The 30-year-old brother was the oldest, and police said he functioned as head of the household when the retired patriarch of the family was on one of his trips to Pakistan, as he was this week.

It may be to early to speculate, but I will anyway. I'm thinking this is yet another "honor killing". One or more of the sisters rebelled in some way against the "head of the household", and the others backed her up. Bang, bang, bang. Honor restored.

As usual, the neighbors are shocked:

Neighbours also described the shootings as baffling, describing the family as "very nice" and "completely normal," noting that they often invited neighbours in for Pakistani food.