Capital punishment is the most premeditated of murders, to which no criminal's deed, however calculated can be compared. For there to be an equivalency, the death penalty would have to punish a criminal who had warned his victim of the date at which he would inflict a horrible death on him and who, from that moment onward, had confined him at his mercy for months. Such a monster is not encountered in private life.
The gallows were used to punish criminals, for instance the pharoahs would chop off people's heads and impale their bodies on poles for birds to eat and the Bible says that one of the reasons Jesus came was so that would not happen anymore because he lifted some sort of curse.