I see no one has yet claimed responsibility for this latest cowardly act. The yanks have a great intelligence gathering system, and, no doubt, the boys and girls at Mossad keep them up to scratch on what's going with assorted Islamic nutbars. But the yanks will find the culprits ... sooner than later hopefully.
The US was expecting some sort of "demonstration" to celebrate the anniversary of the birth of Kim Il-sung. Maybe this was it.
Whatever, it's a vicious, cowardly act that will be punished ... Cashy is right. Yanks take this kinda stuff real serious. And there is no outside authority like "world opinion" or the EU Parliament to cramp their style.