The capital punishment can be considered a valid punishment in multiple cases such as: in case of horrible crimes like mass killings, terrorist attacks, etc. And also death penalty is considered valid in cases of regular law breaking.
The law and order should sentence capital punishment to criminals who have committed heinous crimes such as organizing an terrorist attack or have committed mass murders. Mass murders means killing of number of innocents individual by criminals who are not mentally stable. And terrorist attacks means killing of people by a terror organizations who want to spread fear among the people. Both these types of criminals should be given the capital punishment. For example, the Indian law and order sentenced death penalty to the criminal who carried out the 26/11 blasts.
Capital punishment is also valid in the case of a criminal being a regular offender of law and order. Regular offender is a person who has organized a horrible crime after serving the punishment of pervious crimes. These type criminals are menace to the society because they do not want peace and harmony among the population. For instance, the US law and order has sentenced some felons who were regularly offending the law and they were sentenced to the ultimate penalty so that they can no longer pose a threat to humanity.
In conclusion, capital punishment can be seen valid in cases of terrorists attacks, mass killings and to criminals regularly committing crimes.