Apostate prophet seeks Quranic wisdom; Leave the murderer's fate in victim's hands?

In answer to the video "The Most Violent and Awkward Quran Verse"

In case of murder, there are several aspects of wisdom in leaving the life of the killer directly at the mercy of the heirs of the murdered person. 

It firstly compensates to some extent the tremendous loss caused, because once the justice system has done its job of exposing the guilty, true justice consits in compensating emotionaly or materialy for those first and foremost concerned, ie the victims themselves. 

The other wisdom in leaving the punishment of the killer in the heirs of the slain person's hands is that in case they adopt the preferred issue of being magnanimous, they do a big favour to the murderer and his family, resulting in many other benefits. 

The prophet waived his right for equal retribution many times against his opponents once he had the power to execute justice

"Whoever suffers an injury done to him and forgives (the person responsible), Allah will raise his status to a higher degree and remove one of his sins” (Sunan al-Tirmidhi).

There are countless traditions about his life illustrating his forgiveness to others, even those caught red handed attempting to murder him. But he had no right to force the believers to be forgiving in similar situations, it would be contrary to the spirit of the law as he would be negating their rights to resort to it should they desire. As already said, although the Quran encourages magnanimity in these cases it can only be from the victim, on his or her own accord, without any pressure or influence from anyone, or without any interference from the authorities. This way, because it is an unexpected, benevolent act, it heals both the victim and the criminal.

The story of Cain and Abel illustrated these points, and others, to the prophet Muhammad's addressees. It was similarily through this story that the gravity of murder was forcefully brought to the Israelites' attention for the first time. This moral principle existed since the dawn of humanity, both Cain and Abel were aware of it, as clearly depicted in the Quranic account. 

Again, the incident between the 2 brothers is not what caused the decree regarding the sanctity of human life to be issued and nowhere does the Quran say so. What it clearly states is that the first time the decree was brought to the Israelites' attention, it was illustrated through that incident. There are many examples whether in the Quran or the Bible where a prophet or sage person reminds his addressees of a universal principle, expressed by others before him.

It being "written upon" the children of Israel is a striking wording stressing its gravity to a people known for their long history of wars with their neighboring nations and bloody inter-tribal conflicts during which very little to no sanctity for human life was given. That is not to mention their persecution and slaying of the most righteous elements of the comunity, their own prophets. That this law was decreed upon the Israelites does not take away its applicability to any murder commited anywhere in the world by subsequent nations. Many laws and notions were prescribed and taught to groups of people prior to Islam, this doesnt take away their applicability to Muslims, unless explicitly stated otherwise. In fact the verse says "whoever slays a soul" not "whoever among you slays a soul". The prophet's companions understood the verse as applying to their own time, Uthman for example is reported to have quoted it as he was under siege, to prevent bloodshed.