China would be my guess, since that is where the first cases seem to have developed.
* who was the original target?
If it was Chinese in origin and if it was developed as a weapon, then Taiwan would be a safe assumption. When they make something for U.S. consumption, they won't do it piecemeal.
* deliberate or accidental release?
Accidental. IMO, most countries that develope these things know that using them can backfire on them in a big hurry.
What would be REALLY interesting is if they can cook up a biological equivalent of a binary weapon. This is where you have virus A and virus B...either of which is harmless by themselves. But if someone who has virus A in their system is exposed to virus B, then the interaction between them produces virus C, which is hidiously leathal. Doing this with a virus, while scientifically interesting, would not likely have any benefit other than making it hard to trace it's origin, since this could also backfire. Usually they just do this with poisons instead...much easier to contain the "splatter."