When a person kills another person, there are three rights that must be fulfilled:
1- Allah’s right.
2- The family of the victim’s right.
3- The right of the victim.
If a person repents, Allah’s right is forgiven.
However, he must ask for the forgiveness of the victim’s family and they have the right to ask for the capital punishment, blood money or to forgive him.
As for the right of the victim, this will be taken on the Day of Judgment by the victim himself. Some scholar say that Allah will satisfy the victim so that he would not take his right from the repented killer.