Tenth: the claim must be directed against one single person and no more. Thus, if the heirs say, “He killed him together with another,” qasāmah is not admissible.

It is not a prerequisite that qasāmah be confined to cases of deliberate murder; because it is a legally recognized proof, it must likewise apply to manslaughter just as it applies to intentional homicide.

Once all ten conditions are fulfilled, retaliation may be exacted on the basis of qasāmah.

The procedure begins with the oaths of the male agnatic heirs of the victim. If they swear, the right arising from the homicide devolves upon all the heirs. Should they refuse, the defendant must then take fifty oaths; if the heirs accept his oaths, he is acquitted. If the defendant refuses to swear, the diyah (blood-money) becomes incumbent upon him. But if the heirs neither swear themselves nor accept the defendant’s oaths, the imam (state authority) pays the diyah for the slain person.

Decision of the Council of Senior Scholars concerning qasāmah
Decision no. 41 dated 13/4/1396 AH states:
“After hearing the materials prepared on the opinions of the scholars and deliberating on the matter, the Council resolved—by majority vote—that those who swear from among the heirs are the mentally competent males, even if only one, whether they are agnates or not. This ruling is based on the report of Sahl ibn Abī Ḥathmah in the two Ṣaḥīḥs, and on the principle that an oath taken in support of a claimed right is prescribed only for the litigants themselves, like all other oaths. Allah alone grants success.”
Council of Senior Scholars