Re: Hear, hear! @werdsmith
As for why the prosecution occurred in the U.S., I believe the reasoning was that some of the banks affected were American ones, and at least some victims were American. From that basis, the FBI felt the crime was at least partially under their jurisdiction. From a legal standpoint, the crime could also be investigated and tried in other countries where victims, either banks or users, were located. It's not all that illogical--cybercrime makes it harder to decide where trial should occur, but if victims are in a country, it is within most agreements on international prosecution that the crime can be tried there.
I don't mean by saying this that I support the actions of the FBI in this case. Although I do think they had the right and even the responsibility to investigate the malware, I would have chosen not to pursue the investigation of this small component in the malware given the circumstances, and I don't think his treatment was particularly justified. My statements above are just intended to explain the rationale for the location of investigations and trials.