THOU SHALT NOT KILL is the first commandment. it isn't any of the following:
THOU SHALT NOT KILL unless the person you are killing has killed someone else.
THOU SHALT NOT KILL unless you do it by proxy in a state execution.
THOU SHALT NOT KILL unless you are killing someone to get at some really bad people.
THOU SHALT NOT KILL unless you are defending yourself.
THOU SHALT NOT KILL unless it is in the first trimester of pregnancy.
THOU SHALT NOT KILL unless you think you are saving more people than you are killing.
THOU SHALT NOT KILL unless someone asks you to kill them or you believe it to be merciful.
THOU SHALT NOT KILL unless you are at war.
it is THOU SHALT NOT KILL, period.
again, i don't consider myself a christian, but i think i abide by this particular commandment more closely than most who say they are. there is a reason why it is the first.