Not really sure I would agree with that. By all accounts, terrorist's funding, in this country at least, has either been shut down or (hopefully), is under very close scrutiny. If this is a Terrorist Cell of a few people, then they can't go the normal route for funding, so why not try for a ransome(of which they have no intention of abiding by).
Or why not ask for a ransome in order to keep the public away from the Terrorist angle? And as for not claiming responsibility for these snipings, I would assume even these murderous dogs know that by doing so they have effectively made it so they could never commit another. Because Vigilanties would be out in huge numbers hunting down anyone who even looked like an ME.
I have enough faith that other than a few nuts on FR, the majority of the American people still aren't stupid enough to do this.