If none of these countries has intelligence suggesting the involvement of an established militant group, that leaves two uncomfortable possibilities: one, that the bombing was the work of a new or little-known overseas group or, two, that it was the work of a Thai group.
Either would be a shocking development. Outside the four southern Malay provinces, where a violent insurgency has killed more than 6,000 people over the past decade, an attack on this scale has never occurred in Thailand.
Much depends on how efficiently the Thai authorities conduct their investigation, and so far their performance has not been encouraging.
There have been conflicting and confusing statements from different officials working for different agencies.
The crime scene was not sealed off for several hours after the explosion. The area around the shrine has now been cleaned up with surprising speed, the bomb crater cemented over, rather than leaving it for further forensic work.