Assuming the ransom request wasn't fake. It's pretty likely that the attack came from outside the US. Law enforcement will probably not be able to help at all.
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.
I don't know how you would get feds to pay attention?