One of the bottlenecks in the debate over capital punishment, is subjective and is connected to how elapsed time can alter perception of the past, causing many to lose touch with the reality of the original event.
For example, someone breaks into your house and is threatening to kill you after already killing someone you know. The police come in and shoot him dead. This is the death penality in real time. Under the real time stresses and circumstances it would be a righteous kill even if shooting exceeds lethal injection.
In the next scenario, the killer has just killed your friend and is about to get you. The police charge in, but now the killer puts down his machete. This surrender will allow time to pass, before we can deal with justice. The final result will come out different, for the same action, because the human brain will average the murder, with whatever illlusion the defense will try to create over many years. Now, the same thing the police did in the first scenario (shooting) would be called excessive if it was done after the time delay and the subjective modification.
An analogy for this special effect of the mind is having a toothache. While it occurs one will be highly attuned to the pain. But six months down the line, one's attitude will change, due to water under the bridge. One might be able to recite what happened , when the tooth throbbed, but the emotion becomes more abstract, since the real time pain is no longer there. It is no big deal now. You might now remember being brave instead of whimpering like a baby in real time; selective conclusion.
The ancients figured out how this special effect works; brain will attempt to repress the original real time data and average over time; water under the bridge. The standard they decided to use was, as you do to others, so it shall be done to you. This keeps justice in real time and truncates the illusion effect of the time average which takes way from the pain of the victim and takes away the atrocity of the criminal.
In that case, justice would require that the killer be killed by the same method he used on his victim. If this meant hacking him up with a machete, so be it. What we do via capital punishment is actaully very humaine, since it waters down the machete hacking punishment into lethal injection. This watering down is due to time averaging, but it least it tries to keep its eye on the ball; real time without dilution illusion.
Some people would consider that wait time you are talking about to be inhumane (many years on death row). If I was on death row, I would much rather just get it over with. Also, think what it does to the revenge crazed loved ones of the victim. They can't put the whole thing behind them and move on, but have to take an agonizing emotional roller coaster ride of appeals and last minute stays and what not, wondering if it will ever end. Then just think of the disappointment if for some reason the execution doesn't happen?