Too soon to say who was responsible. Lived and worked in the region for 10-years mid-80's/mid-90's. As sb_73 said, the Muslim insurgency is basically in the south, so one cannot yet be certain it was them. The current military regime has its enemies in the north too. I am not at all sure that it is specifically an attack against foreigners, as hundreds of Thai people pray daily for good luck by the Erawan Shrine. Lived at a big hotel right next door to the Hyatt on Rajdamri Road first six months of stay, so wife and I know the Erawan Corner very well. Very tragic, the Thais are basically decent people who detest violence in any form.