We could go Singapore's route where murder carries a mandatory death sentence. This results in a murder rate of almost zero(and therefore executions are rare), so in the end, its almost win-win.
Or it would mean that there are a lot more innocent people getting executed instead of the real murderer AND murderers will make sure to kill all witnesses and will resist the police to death since getting arrested will mean certain as well, so there is no reason for them to surrender.
How often does either scenario happen? I think that's something important to note.
The fact that death penalty still needs to be used in the countries that have death penalty means that it is not a complete deterrent. Singapore may be an exception, but generally people will still commit crimes that carry death penalty.
Or we could take a page from Scandinavian countries and actually rehabilitate our prisoners.
I for one support that (although we have morons complaining how the system cuddles the prisoners by treating them like human beings.)
Some criminals just can't be rehabilitated. Take Peter Woodcock, for example.
But that still does not mean that we should stop treating them like human beings. In an ideal situation the justice system will try to rehabilitate the convicted criminals and IF after their sentence is up they are still deemed to be unable to be returned to society they will be kept detained further. Usually this is done to those who are so insane or simply so unstable that they need to be kept in an insane asylum.
But simply locking someone into a tower and throwing away the key will take away their chance to make amends and usually just makes them worse. Keeping them detained (despite what some people believe, having your freedom taken away IS a punishment to most people) and re-educating them or offering psychiatric treatment will perhaps let them learn the error of their ways AND make it less likely for them to commit more crimes if/when they are released.
There was actually a study about Finnish convicts who had been serving life sentence. Which in Finland is usually 12-14 years before being pardoned. (Before the pardon could only come from the president, now there is an actual board with professionals who will judge wether or not the person can be released.)
There is like 22% of them who will commit more crimes, compared to the average of 54,7% of other convicted criminals (this includes all jail sentences, so many are quite short and for minor crimes.) who will commit more crimes. Clearly the system is not perfect but the life sentence is given to the worst kinds of criminals and even then most of them become law abiding citizens.
Source:
http://www.rikosseuraamus.fi/material/attachments/rise/julkaisut-monisteetjaraportit/c93POV0xz/2014-5_ELINKAUTISVANKIEN_UUSINTARIKOLLISUUDESTA.pdf (Mostly in Finnish but the abstract on the third page is in English.)
The point that I am trying to make with this is that sometimes rehabilitation works and it may even work for murderers (the amount of murderers is quite high among those that serve life sentence in Finland) AND if we later find out that they were innocent we can at least apologize and their life will go on. (Though I also see that Finland does have a problem with repeat offenders in the less serious crimes. But there is a difference between long sentence and inhuman treatment.)
