God is the one who created us all. It is His prerogative to give life, and take it back. None on this earth has the right to inflict death on anyone else. If we go through the religious literature, across historic and cultural distinctions, we find that life is considered as supreme.
All the moral, ethical, and legal codes are designed to safeguard life. The story of Abel and Cain tells us the eternal lesson of what it means to kill a soul in the sight of God. Referring to the same story God emphatically makes it clear in His last word, The Quran, that one who kills a soul kills the entire humanity. The way this teaching has been eternally saved in the holy Quran speaks of the importance of human life.
The act of killing an innocent person is unpardonable. The punishment for this crime in the hereafter is hellfire, and that too eternal. The life of Prophet Muhammad (SAW) tells us how even a slightest harm to anyone would turn the Prophet restless. He would even feel for the animals, and thus the teaching that whenever an animal is found tired one should dismount, and allow the creature to take rest. All the religions that people around the globe follow lay emphasis on not harming any soul.
Unfortunately there are people who forget this divine teaching and resort to harming others. Sometime ignorance and evil emotion makes them cross the final barrier, and they snatch an innocent life. In the light of Quran there is no bigger crime that one can commit against mankind. The Prophet of mercy (SAW) taught us the value of life.
If we are his followers we must be on the side of the oppressed, and in case an innocent is killed we should feel the pain. We must remember the divine words:
Because of that We ordained for the Children of Israel that if anyone killed a person not in retaliation of murder, or (and) to spread mischief in the land - it would be as if he killed all mankind, and if anyone saved a life, it would be as if he saved the life of all mankind. (5:32)