Praise be to Allah.
Murder (killing a person deliberately), if the victim is a believer, is one of the greatest of major sins, because Allaah says (interpretation of the meaning):
“And whoever kills a believer intentionally, his recompense is Hell to abide therein; and the Wrath and the Curse of Allaah are upon him, and a great punishment is prepared for him”
And it was narrated that the Prophet (peace and blessings of Allaah be upon him) said:
“A man will continue to be sound in his religion so long as he does not shed blood which it is forbidden to shed.”
If you killed a believer deliberately, then there are three rights which are connected to that: the rights of Allaah, the rights of the victim and the rights of the victim’s next of kin.
With regard to the rights of Allaah: if you repent sincerely to your Lord, then Allaah will accept your repentance, because He says (interpretation of the meaning):
“Say: “O ‘Ibaadi (My slaves) who have transgressed against themselves (by committing evil deeds and sins)! Despair not of the Mercy of Allaah, verily, Allaah forgives all sins. Truly, He is Oft-Forgiving, Most Merciful” [al-Zumar 39:53]
With regard to the rights of the victim, he is not alive so you cannot put things right with him. The matter has to wait until the Day of Resurrection, i.e., the settling of scores with you on behalf of the victim will take place on the Day of Resurrection. But I hope that if your repentance is correct and is accepted by Allaah, then Allaah will compensate the victim with what He wills of His bounty until he is satisfied, and you will be reprieved.
With regard to the rights of the victim’s next of kin, which is the third right, you cannot be absolved of this until you hand yourself over to them. Therefore you have to hand yourself over to the victim’s next of kin, and tell them that you are the one who killed him, then they have the choice. If they want to they can exact vengeance upon you, if the conditions of qasaas are met; or if they want to they may take the diyah (blood money) from you; or if they want to they can forgive you.