Yes. I wouldn’t say beyond any doubt, but for practical purposes very nearly so. As I’ve argued before, there are three bodies of law (potentially) relevant for assessing the legality of a targeted killing: the jus ad bellum, IHL, and human rights law.
This is an answer to the question that was too impolitic to give attention.
I’m not saying I feel great about OBL being sanctioned, I’m just saying I had a question and for a law professor and another law professor answered it.