2 Samuel 13:21

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

When David heard of Amnon's shameful crime, he was very angry. The law pronounced death upon the adulterer, and Amnon's unnatural and incestuous crime made him doubly guilty. Though angry, he permitted his first-born son to pass unpunished and unrebuked, for being self-condemned for his own sin he failed to bring the offender to justice.

This account belongs to the wrongs in David's family that continually brought the consequences of his own wrongdoing to mind. His failure left the case to Absalom as the natural protector of his foully wronged sister. Absalom concealed his purpose of revenge for two full years and then avenged the great crime by having the drunken Amnon slain by his command at a feast of the king's sons.