(Digest 48.5.21; 48.5.22; 48.5.23 pr.-2, 4; 48.5.24 pr.-4; 48.5.25 pr.-3; 48.5.26 pr.; 48.5.27 pr.-1. L)
48.5.21 (Papinian, On Adultery, book 1) The right is granted to the father to kill an adulterer with a daughter while she is under his power. Therefore no other relative can legally do this, nor can a son in paternal power, who is a father.
48.5.22 (Ulpian, On Adultery, book 1) (pr.) Hence it can happen that neither the father nor the grandfather can kill the adulterer. This is not unreasonable, for he cannot be considered to have anyone in his power who is not subject to his power.
48.5.23 (Papinian, On Adultery, book 1) (pr.) In this law, the natural father is not distinguished from the adoptive father. (1) In the accusation of his daughter, who is a widow, the father is not entitled to the preference. (2) The right to kill the adulterer is granted to the father in his own house, even though his daughter does not live there, or in the house of his son-in-law … (4) Hence the father, and not the husband, has the right to kill the woman and any adulterer; for the reason that, in general, paternal affection is solicitous for the interests of the children, but the heat and impetuosity of the husband, who decides too quickly, had to be restrained.
48.5.24 (Ulpian, On Adultery, book 1) (pr.) What the law says, that is, ‘if he finds the adulterer in his daughter,’ does not seem to be superfluous; for it signifies that the father shall have this power only if he surprises his daughter in the very act of adultery. Labeo also adopts this opinion; and Pomponius  says that the man is killed when caught in the very performance of the sexual act. This is what Solon and Dracho mean by “in the act” (en ergôi).
(1) It is sufficient for the father for his daughter to be subject to his power at the time when he kills her, although she may not have been at the time when he gave her in marriage; for suppose that she had afterwards come under his power.
(2) Therefore the father shall not be permitted to kill the parties wherever he surprises them, but only in his own house, or in that of his son-in-law. The reason for this is, that the legislator thought that the injury was greater where the daughter caused the adulterer to be introduced into the house of her father or her husband.
(3) If, however, her father lives elsewhere, and has another house in which he does not reside, and his daughter is caught there, he cannot kill her.
(4) Where the law says, ‘He may kill his daughter at once,’ this must be understood to mean that having today killed the adulterer he cannot reserve his daughter to be killed some days later; and vice versa; for he should kill both of them with one blow and one attack, being inflamed by the same resentment against both. But if, without any connivance on his part, his daughter should take to flight, while he is killing the adulterer, and she should be caught and put to death some hours afterwards by her father, who pursued her, he will be considered to have killed her immediately.
48.5.25 (Macer,  Criminal Proceedings, book 1) (pr.) A husband is also permitted to kill a man who commits adultery with his wife, but not everyone without distinction, as the father is; for it is provided by this law that the husband can kill the adulterer if he surprises him in his own house (but not in the house of his father-in-law), nor if the adulterer was formerly a pimp; or formerly exercised the profession of an actor or appeared on the stage to dance or sing; or had been convicted in a criminal prosecution and not been restored to his civil rights; or if he is the freedman of the husband or the wife, or of the father or mother, or of the son or the daughter of either of them (nor does it make any difference whether he belonged exclusively to one of the persons above mentioned, or was held in common with another), or if he is a slave.
(1) It is also provided that a husband who has killed any one of these must dismiss his wife without delay.
(2) It is held by many authorities to make no difference whether the husband is his own master, or a son in paternal power.
(3) With reference to both parties, the question arises, in accordance with the spirit of the law, whether the father can kill a magistrate, and also where his daughter is of bad reputation, or a wife has been illegally married, whether the father or the husband will still retain his right; and what should be done if the father or husband is a pimp, or is branded with ignominy for some reason or other. It may properly be held that those have a right to kill who can bring an accusation as a father or a husband.
48.5.26 (Ulpian, Lex Julia on Adultery, book 2) (pr.) It is provided as follows in the fifth section of the Julian law: ‘That where a husband has caught an adulterer in the act of sexual intercourse with his wife, and is either unwilling or not allowed to kill him, he can hold him lawfully and without deceit for not more than twenty consecutive hours of the day and night, in order to obtain evidence of the crime.’
48.5.27 (Ulpian, Disputations, book 3) (pr.) A woman cannot be accused of adultery during marriage by anyone who, in addition to the husband, is permitted to bring the accusation; for a third party should not annoy a wife who is approved by her husband, and disturb a quiet marriage, unless he has previously accused the husband of pimping (for his wife). (1) When, however, the charge has been abandoned by the husband, it is proper for it to be prosecuted by another.On Adultery
23. Primarily a teacher and writer (no mention is made of his holding an imperial post), Sextus Pomponius lived in the mid-second century A.D. and wrote influential commentaries on Q. Mucius, Sabinus, and the Praetor’s Edict.
24. Little is known of Aemilius Macer other than that he was active in the early third century A.D. and was a member of a senatorial family.