The Koran allows for the death penalty but also its aboloshing provided that the murderer is kept from society either by exile or prison etc.
Chapter 5 tells us:
27. Recite to them the truth of the story of the two sons of Adam. Behold! they each presented a sacrifice (to Allah.: It was accepted from one, but not from the other. Said the latter: "Be sure I will slay thee." "Surely," said the former, "(Allah) doth accept of the sacrifice of those who are righteous.
28. "If thou dost stretch thy hand against me, to slay me, it is not for me to stretch my hand against thee to slay thee: for I do fear Allah, the cherisher of the worlds.
29. "For me, I intend to let thee draw on thyself my sin as well as thine, for thou wilt be among the companions of the fire, and that is the reward of those who do wrong."
30. The (selfish) soul of the other led him to the murder of his brother: he murdered him, and became (himself) one of the lost ones.
31. Then Allah sent a raven, who scratched the ground, to show him how to hide the shame of his brother. "Woe is me!" said he; "Was I not even able to be as this raven, and to hide the shame of my brother?" then he became full of regrets-
32. On that account: We ordained for the Children of Israel that if any one slew a person - unless it be for murder or for spreading mischief in the land - it would be as if he slew the whole people: and if any one saved a life, it would be as if he saved the life of the whole people. Then although there came to them Our apostles with clear signs, yet, even after that, many of them continued to commit excesses in the land.
33. The punishment of those who wage war against Allah and His Messenger, and strive with might and main for mischief through the land is: execution, or crucifixion, or the cutting off of hands and feet from opposite sides, or exile from the land: that is their disgrace in this world, and a heavy punishment is theirs in the Hereafter;
34. Except for those who repent before they fall into your power: in that case, know that Allah is Oft-forgiving, Most Merciful.
Here the Koran tells us about the story of Adam's son where one apparently killed his brother. This crime of murder therefore has been there from day one. The Koran then says that a crime like murder is as if someone killed the whole of mankind and if he saves a life it is as if he saved the whole world. I think its because if it was the other way around then none of us will be here since we are(I think) the ancestors of the surviving son. The murder of our father is like the murder of all his children and their children too. Anyways the Koran says even after that the Jews commited excesses since the Talmud spined this verse and claimed this prohibition is for Jews and not mankind but this not the point here.
Anyways we will look at what the Koran said regarding the punishment for murder:
5.33. The punishment of those who wage war against Allah and His Messenger, and strive with might and main for mischief through the land is: execution, or crucifixion, or the cutting off of hands and feet from opposite sides, or exile from the land: that is their disgrace in this world, and a heavy punishment is theirs in the Hereafter
Here the Koran gives among the punishments:
or exile from the land:
This means the Koran does allow for abolishing the death penalty. Some have looked at this verse:
2178-179. O ye who believe! the law of equality is prescribed to you in cases of murder: the free for the free, the slave for the slave, the woman for the woman. But if any remission is made by the brother of the slain, then grant any reasonable demand, and compensate him with handsome gratitude, this is a concession and a Mercy from your Lord. After this whoever exceeds the limits shall be in grave penalty. In the Law of Equality there is (saving of) Life to you, o ye men of understanding; that ye may restrain yourselves.
They then say this implied that a murderer should get death as punishment. However the verse is implying compensation since how else could you understand the verse? If a free man kills a slave then you don't kill a slave for punishment. It seems the verse is talking about equity. Anyways it also says that remission can be made and monetary compensation could be taken. I think this verse is talking about man slaughter and not murder as the verse in chapter 5 is talking.
Others have pointed to the eye for an eye verse:
5.44-48. It was We who revealed the law (to Moses): therein was guidance and light. By its standard have been judged the Jews, by the prophets who bowed (as in Islam) to Allah.s will, by the rabbis and the doctors of law: for to them was entrusted the protection of Allah.s book, and they were witnesses thereto: therefore fear not men, but fear me, and sell not my signs for a miserable price. If any do fail to judge by (the light of) what Allah hath revealed, they are (no better than) Unbelievers. We ordained therein for them: "Life for life, eye for eye, nose or nose, ear for ear, tooth for tooth, and wounds equal for equal." But if any one remits the retaliation by way of charity, it is an act of atonement for himself. And if any fail to judge by (the light of) what Allah hath revealed, they are (No better than) wrong-doers. And in their footsteps We sent Jesus the son of Mary, confirming the Law that had come before him: We sent him the Gospel: therein was guidance and light, and confirmation of the Law that had come before him: a guidance and an admonition to those who fear Allah. Let the people of the Gospel judge by what Allah hath revealed therein. If any do fail to judge by (the light of) what Allah hath revealed, they are (no better than) those who rebel. To thee We sent the Scripture in truth, confirming the scripture that came before it, and guarding it in safety: so judge between them by what Allah hath revealed, and follow not their vain desires, diverging from the Truth that hath come to thee. To each among you have we prescribed a law and an open way. If Allah had so willed, He would have made you a single people, but (His plan is) to test you in what He hath given you: so strive as in a race in all virtues. The goal of you all is to Allah. it is He that will show you the truth of the matters in which ye dispute;
This is talking about what was revealed in the Torah, anyways it also says one can remit the retaliation and seems to talk about equity once again. However murder is different in the sense that society as a whole could be threatened and even if the family pardons the murderer society would not want this person roaming the streets where he can kill again. It also says the Gospel should be followed and yet we see no communal laws laid out in the Gospel. I think the verse is talking about religious laws should be taken from the Torah, Gospel and Koran. And as I said before, the Jews left the Torah for the Talmud, the Christians left the Gospel for the trinity and Muslims left the Koran for the Hadith. Thats is what the verse was trying to warn about and not murder.
I don't think those verses are talking about murder, I think the verse I showed about the sons of Adam is talking about murder. The term "those who wage war" here means opposing and not actual fighting such as the war on drugs or war on poverty. The Koran uses a different verbal term for actual fighting. It uses "qital" and not "harb" as this verse uses. This is so since fighting would mean prisoners of war and the Koran already has ordered that prisoners should either be set free or have a ransom on them. Punishing prisoners is absolutely forbidden in the Koran.
So there is no reason why from a Koranic point of view why death penalty can not be abolished as long as the murdere is exiled from the land. Prison as we know is a form of exile from community.
Real Islam is only Koran!
Koran is peace