Possibly I can give a different perspective to the 'death penalty' argument.
Having been a tutor in the education dept of a prison that has a large population of 'lifers' , I have talked one 2 one with at least 9 murderers.
They all have one thing in common. The actual murder was a 'one off' a moment of temporary insanity or loss of temper in the heat of an argument.
Not one of them, for a single second, thought '' hang on! , if I do this I will go to jail'' There was no thought in their heads other than the 'rage of the instant'.
Yes there are a few, very very few, who are calculated intentional killers, I never met one!
I am totally certain that the death penalty does not deter murder, it just acts as appeasement to the victims family and society in general, so satisfying the demand for 'justice to be done'.
A society that kills people by order of a court is no more 'civilized' than the killers themselves. This applies particularly to the USA !!! where an overwhelming majority of those found guilty of murder and sentenced to death are black/poor /uneducated/ illiterate and so unable to afford proper legal defense!