[Xylakant]

Why not? The US. Law enforcement obviously doesn't have jurisdiction, but as long as a DOS is illegal in the country that the attacker sits in, the US Law enforcement should investigate and hand off to a partner agency in that country, acting as liaison and serving a request for extradition.

It's a different matter if the attacker is based in a country where DOS are legal or that doesn't have any extradition treaty with the US, but that still needs to be established.