I meant an infallible way to find the guilty party in a crime. Such simple, obvious measures as a complete national DNA and fingerprint database which the police have access to, 24 hour surveillance with facial recognition in all public spaces, and a legal obligation -on pain of imprisonment — to give a full and truthful answer to any question posed by a duly warranted officer of the law. You can have civil liberty OR a crime-free society, not both.
As for who to release, that’s easy! The fools and the broken.
Fools: The kid who takes part in an illegal street race, or holds up a shop on a dare, for instance. The guy who gets drunk and gets in a fight. Minimum sentence and some education, they’ll be OK.
Broken: The poor schmuck who comes home, finds his wife in bed with his best friend and shoots them both. The abused wife who puts a knife between the bastards ribs. The victim of bullying who finally has enough and lashes out. Those people need help, not punishment.
But the fraudster, the bank robber, the killer for profit, the con man….Those who deliberately plan to break the law for their own advantage. They cannot be rehabilitated — they made their choice in sound mind and awareness of the possible consequences. If they think they can get away with it again, they’ll do it again. If they can play the system, they'll play it. You can either lock them up for life, or make prison so hellish that they’ll do anything to avoid going back. Make it an isolating, mind-numbing, health-wrecking experience they’ll take years to recover from and would rather die than return to. You know, actual punishment.
As to the serial killer, the mass-murderer, the rapist, the child-molester. These are no longer fit to be accounted human. Dangerous animals who should be put down.