Captial punishment is the only fitting punishment for murder. A central principle of a society is that every person has a right to “life”. That means nothing could be more important than this. Within that framework, murduring should be unexcusable under any circumstances. A murderer is hard to rehabilitate; he can easily repeat his crime.
And goverment has a big responsibility that defend people from such danger. For this reason, the death penalty is essential to a just and moral society. Anyone who denies the right of life by unjustly taking. And, the standard of judgement has to be the punishment fits the crime.