Absalom had an outing in Baal Hazor with his sheepshearers. He invited the king and his sons, but David declined, not wanting to be a burden to Absalom. Absalom asked for him to allow Amnon to attend with him, and David consented. Absalom instructed his servants to strike Amnon when he got drunk. Once Amnon was killed, all the other sons of David left on mules. Word got back to David that all the sons of the king had been killed, and David tore his clothes in mourning. However, another servant came and told David that only Amnon was killed, and that Absalom had plotted this ever since Amnon attacked his sister Tamar.
Although, revenge is not the best policy, it is important to understand that sin is expensive. What you sow, you will reap. In this case, Amnon raped his sister and then shamed her by sending her away. He was murdered in retribution. Sin is never an isolated incident. Sin will come home to roost! While God will forgive sin, the effects of sin may linger. Avoid sin and follow God to be blessed beyond measure!