The thing is, if you had all that evidence, it would probably be quite straightforward to establish a motive. If you had all that and can't establish a motive, well, it'd probably not be as clearcut as you'd make it out to be in your hypothetical. We may know that the person did the action, but we wouldn't know exactly how to attribute their level of guilt. If in legal terms I am wrong about this, I'd like some examples of convictions where motive was never determined. Maybe accident isn't the best word choice. Rather, no established motive would indicate that the case is not as obvious as it appears.