Immanuel Kant Quote

Even if a civil society were to be dissolved by the consent of all its members (e. g., if a people inhabiting an island decided to separate and disperse throughout the world), the last murderer remaining in prison would first have to be executed, so that each has done to him what his deeds deserve and blood guilt does not cling to the people for not having insisted upon this punishment; for otherwise the people can be regarded as collaborators in his public violation of justice.

Kt6:333 - Metaphysics of Morals (1797)