Is the execution—as retribution—of a murderer who killed a group of people considered expiation for all his crimes, or for only one crime?

Execution as retribution (qisas) occurs only once, even if a person kills an individual or a group. The prevalent opinion among scholars is that a killer can repent. If the killer repents and qisas is carried out, Ibn al-Qayyim believes that Allah compensates the victim through His complete forgiveness of the killer, because sincere repentance obliterates what preceded it. Qisas combined with sincere repentance expiates the killer's sin, and he will not be held accountable in the Hereafter, whether he killed one person or a group. Ibn Hajar holds that the sins of a victim unjustly killed are expiated by their death, and this is a great right for them, citing Hadiths such as: "Indeed, the sword is an obliterator of sins."