Additional: The paladin's action was human. Humans do things certain parties would much rather they didn't. They get angry, they lash out. They kill people in a rage. No one can strictly adhere to a code of laws, because codes of law are devised by people who let their ideology overrule their good sense.
Any legal system that disregards this will, sooner or later, fail.
Any legal system that disregards this will, sooner or later, fail.