Is the repentance of someone who participated in a murder and masterminded its concealment without turning himself in to the police accepted?

Killing a believer intentionally is one of the gravest major sins, and it entails three rights: the right of Allah, the right of the slain, and the right of his guardians. The right of Allah is forgiven through sincere repentance. The right of the slain remains until the Day of Resurrection. As for the right of the guardians, one is not absolved of it except by surrendering oneself to them, and they have the choice between retribution (qisas), blood money (diyah), or forgiveness.