It shows that the justice system has no sympathy for the criminals.
When criminals escape from the capital punishment, they repeat their crimes and take more innocent lives.
The availability of modern testings such as DNA testing reduces the chances of punishing the innocents; therefore, capital punishment can be an effective tool to control the crimes.
The death penalty can address the problem of overpopulation in the prisons.
It gives closure to the families of the victims who have already suffered a lot.