Capital punishment, whilst I agree that there will be the odd case of injustice it will also act as a deterrent. So from a numbers perspective the drop in serious crimes should overall result in fewer cases. You could also limit the potential for miscarriage of justice by setting a time limit of 5 years or so whereby any new evidence materialising can be submitted.
Generally countries who have a harsh attitude to crime and punishment have much lower crime rates.
Personally I would accept the loss of a few individuals if overall the safety of the general population was greatly improved.
I would suggest that the current soring knife crime epidemic would be fixed overnight.
Cowardly low life would not be as brave