You can tell I'm getting to the nitpicking and rewording stage of writing an assignment for the OU when I go on flights of sfnal legal fantasy instead.

A bunch of senior members of the judiciary have a time machine. When a miscarriage of justice is discovered, they use the time machine to wind the unverse back to before the miscarriage. Obviously this looks splendid, and nobody in the rewound universe (handwave handwave) suffers the consequences of long prison times.

Unfortunately, a convicted criminal learns of the existence of this machine and on his release uses it to rewind so he committed the perfect crime...