All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
For repentance from the sin of murder to be valid, it is not enough to simply stop the act, feel sincere remorse, and firmly intend not to repeat it. The murderer must also allow the rightful claimants of Qiṣaṣ (retribution) or Diyah (blood money) the opportunity to obtain their due right.
Repentance is invalid in the case of lying or evading the obligations resulting from (willful) killing, such as Qisas or paying Diyah.
It is mentioned in Rawdat at-Talibin (a book in the Sahfi’i school of jurisprudence):
Our companions (the Shafi’i scholars) said: “Repentance between the servant and Allah the Almighty is that in which a sin is forgiven. It consists of feeling remorse for the act, ceasing the act immediately, and resolving never to return to it… If the sin involves a non-financial right of another person, such as Qisas or the legal punishment for Qadhf (slander), the person must surrender himself to the one entitled to the right and enable him to obtain his due right. If the rightful person does not know, then in the case of Qisas, he (the murderer) must inform him, saying: “I am the one who killed your father, and I am liable for Qisas. If you wish, demand Qisas; and if you wish pardon me.” [End quote]
Allah Knows best.