In the King James Version, Exodus 20:13 is mistranslated. In that Bible, it says:
‘Thou shalt not kill.’
However, this is incorrect. Nearly every other translation says ‘murder.’ Why? The word used in the Greek Septuagint is phoneuseis, which means ‘murder,’ and not simply ‘kill.’ It is a similar story with the Hebrew word.
This makes sense, because killing, in the form of execution, was mandated in the law itself. Execution was even the punishment for murder! At Exodus 21:12 in the Greek Septuagint it literally says:
‘Thananato thanatoustho,’
‘To/death let/him/be/put/to/death!’
So Exodus 20:13 could not mean ‘Thou shalt not kill,’ because then the law would contradict itself. On the contrary, God’s Law to Moses very emphatically said that murderers should be executed.
In the modern day, some Christians have used the mistranslated words ‘Thou shalt not kill’ in political campaigns to argue against the death penalty. However, as we saw, it does not say ‘kill,’ it says ‘murder,’ and killing in the form of execution was part of the law itself.