As part of criminal justice reform, a system that allowed reductions in punishments following substantial assistance in investigations or prosecutions was considered, but its introduction was finally deferred by the Ministry of Justice. The MOJ may undertake a reintroduction of this system in the near future. However, before this system can be introduced, the reasons for a defendant who is cooperating in a criminal investigation being entitled to a reduced punishment must be considered. One hypothesis is that the criminal liability of the defendant decreases if the defendant has contributed to a successful investigation. Another is the political reason of providing an incentive to the defendant for voluntary cooperation in criminal investigations. This article reviews the discussion of the Legislative Council, New Era’s Criminal Justice System Special Subcommittee on this matter, and considers the efficacy of this system.