Matthew Poole and continuators on 2 Samuel 13:21

21 ¶ But when king David heard of all these things, he was very wroth .

To wit, with Amnon: whom yet he did not punish, at least so severely as he should: either from the conscience of his own guilt in the like kind; or, from that foolish indulgence which he oft shewed to his Children: or, because the case was perplexed: for if he had been put to death for the Fact, by vertue of that Law, Deut. 22. 23, 24. she also, who was innocent, must have died with him, because she did not cry out: although indeed that Law did not reach the present case, Tamar not being betrothed to an Husband: and for the following Law concerning a Virgin not betrothed, that could have no place here: he could not force Amnon to Marry Tamar, because that Marriage had been incestuous.