A Turkish national was arrested by police yesterday in connection to the bombing, was found with 10 fake passports and bomb making material. Not suspected to be the actual bomber, though.
Turkish involvement would suggest a connection to the deportation of Uyghur refugees to China two months ago. If you recall there were riots in Turkey over that incident, and the Thai embassy was attacked. It would also provide an answer to the question of who in Thailand would bomb a Buddhist shrine (answer: someone who was neither Thai nor Buddhist).
The turkish passport found is a very fake one, so its not clear what nationality he is.
