Amnesty –forgiving all of the current and previous violators but renewing a threat to punish future violators– always seems like a reputation fail. If we are granting amnesty today then doesn’t that signal that we will eventually be granting amnesty again in the future?
But there is at least one environment in which a once-only amnesty is incentive compatible and effective: when crime has bandwagon effects. For example, suppose there’s a stash of candy in the pantry and my kids have taken to raiding it. I catch one red-handed but I can’t punish her because she rightly points out that since everybody’s doing it she assumed we were looking the other way. A culture of candy crime had taken hold.
An amnesty (bring me your private stash and you will be forgiven) moves us from the everyone’s a criminal because everyone’s a criminal equilibrium to the one in which nobody’s a criminal. The latter is potentially stable if its easier to single out and punish a lone offender than one of many.