You could commit a crime then claim not to remember. How could it be proven otherwise? If the science exists to know for a fact that you don’t remember a specific event then the science likely exists to also wipe that event from your memory. You could commit a crime then deliberately wipe your memory of it to escape punishment.

necessarily if they did it, they possess the same identity as before; they are the same person who is guilty, even if they are not the same person who was previously unrepentant or now possesses no knowledge of the crime or intent

morally in a way before God in a Christian view I think they may not be able to “merit” further punishment if they are not of a sound mind