Murder is the unlawful killing of another. "Innocence" has nothing to do with it, and for good reason. Society can't afford to have shooters roaming around judging innocence for themselves.
No one is asking you to feel "sadness." This writer is asking you to consider that the shooting was wrong.
I don't think the word “murder” in the previous post was about how Man defines it in his laws, but the meaning of the sixth Commandment:
“You shall not murder.”
The meanings are not necessarily the same. As I said before, killing to save your own, or another's life is lawful under God's Commandment.