Pretty much, yes. The US could declare them Persona Non Grata but only Saudi Arabia could prosecute. While the persons themselves may not step foot in the USA. Saudi Arabia has a huge amount of assets in the USA that are not protected by Diplomatic immunity and can be seized by US courts for damages, penalties, costs etc. if it can be proved the owners of the assets are guilty. While money may not help those that died its loss would hurt those who aided those that launched the attacks.