Throwing grenades into a school? Mother of god, is there no depth to which people will plunge?
This looks more like a part of the ongoing violence in Karachi, and not related to TTP or other militant outfits. Apparently the principal was a member of the ANP, and had been receiving threats for some time. So this is probably part of the ongoing political violence. I would venture a guess and say that nobody would claim responsibility for this. It would be difficult for any group to justify such an act, unlike the Malala incident, in which the Taliban had a message to send. (Not that that was justifiable either.)
This looks more like a part of the ongoing violence in Karachi, and not related to TTP or other militant outfits. Apparently the principal was a member of the ANP, and had been receiving threats for some time. So this is probably part of the ongoing political violence. I would venture a guess and say that nobody would claim responsibility for this. It would be difficult for any group to justify such an act, unlike the Malala incident, in which the Taliban had a message to send. (Not that that was justifiable either.)