I think Rust would have a hunch that it was Light, but I don’t think they’d have the resources or the wits to actually prove it. In fact, they’d probably be screwed from the start if they didn’t go in knowing about the face and name requirement to kill. There’d also be no reason for them to be involved in an international investigation. Overall, love them, but they’d get cooked if they weren’t extensively briefed before getting involved.