What would be the difference between this futuristic case and: - Bob kidnapping Alice - Alice not being found - Bob's guilt of the kidnapping is proven in court

What would be the difference between this futuristic case and: - Bob kidnapping Alice - Alice not being found - Bob's guilt of the kidnapping is proven in court Bob could claim e.g. that she escaped after being kidnapped and he's no longer aware of where she is. Alice's dead body can still be found at some point, which could prove that Bob killed Alice; or she can be found alive, but because of any reason did not want to be found.