I’m not so sure it’s feasible to carry out an assassination with enough secrecy that no one could know you did it. It’s hard to keep a secret if the world’s best intelligence agencies are all highly motivated to figure it out! Now, your word choice was “no one could necessarily _prove_ you did it,” but even if it could not be proven in say an international tribunal, if other countries knew that my country did it, they could retaliate.
I’m not so sure it’s feasible to carry out an assassination with enough secrecy that no one could know you did it. It’s hard to keep a secret if the world’s best intelligence agencies are all highly motivated to figure it out! Now, your word choice was “no one could necessarily _prove_ you did it,” but even if it could not be proven in say an international tribunal, if other countries knew that my country did it, they could retaliate.