Rickard was a vengeful man who held on to grudges. However, his actions were natural. When Catelyn learned that her sons Bran and Rickon got killed in the Sack of Winterfell, she freed Jaime and asked Brienne to take him to King's Landing. As Jaime killed Rickard's sons, he was angry at Catelyn's actions; this caused him to kill two of Robb's hostages.