Just because you legally killed someone doesn't mean it's not murder. Did Hitler murder lots of Jews? Did Stalin murder enemies of the people? Did Anglo-settlers in the USA murder countless slaves and native peoples?
"Murder is the unlawful killing, with malice aforethought, of another human, and generally this premeditated state of mind distinguishes murder from other forms of unlawful homicide (such as manslaughter)." -- wikipedia
The question of whether a set of laws is legitimate is another question.
The question of whether a set of laws is legitimate is another question.