Retaliation is carried out in the same manner as the murder
The sacred month is for the sacred month, and for the prohibited things, there is the Law of Equality [Qisâs]. Then whoever transgresses the prohibition against you, you transgress likewise against him. And fear Allâh [swt], and know that Allâh [swt] is with Al-Muttaqûn (the pious].[8]
And if you punish [your enemy, O you believers in the Oneness of Allâh (swt)], then punish them with the like of that with which you were afflicted. But if you endure patiently, verily, it is better for As-Sâbirin [the patient ones, etc.][9]
The retaliation is carried out in the same manner as the murder to ensure equality and reciprocity.
Retaliation may be forgiven for blood-money
O you who believe! Al-Qisâs [the Law of Equality in punishment] is prescribed for you In case of murder: the free for the free, the slave for the slave, and the female for the female. But if the killer is forgiven by the brother [or the relatives, etc.] of the killed against blood money, then adhering to it with fairness and payment of the blood-money, to the heir should be made in fairness. This is alleviation and a mercy from your Lord. So after this whoever transgresses the limits [i.e. kills the killer after taking the blood-money], he shall have a painful torment. And there is [a saving of] life for you in Al-Qisâs [the Law of Equality in punishment], O men of understanding, that you may become Al-Muttaqûn [the pious].[10]