I disagree laz.
If a soldier in the US armed forces is told to terminate a target and does so.
Was that killing Murder?
Is a convicted felon facing the electric chair, lethal injection, etc being killed or murdered?
My point is that society & civilization decides what killing is "lawful". And yes its wrapped in strict legal terms for a reason. To keep just anyone who wants someone else dead from going out and killing them.
Someone who on their own goes out and kills another person with or without just cause. THATS murder most foul. Not because the person died, not because he had cause or not. But because the killer did it on their own, without the sanction of society, or under society's orders.