I had the same question and concluded that HE meant that thou shalt not murder or take innocent blood. There is evidence throughout the OT of military campaigns i.e. nation against nation and even in the NT God said that this would be. Jesus also said that we should turn the other cheek if we are smitted on the right one but it appears He was talking on an individual level when we are taken by those in authority i.e. by the police as He was. In all cases we are called to love, so if one is in battle if a life can be spared you don't just take that life, that would be murder. I just saying...
This lesson was very inspiring for me to pay close attention to understanding the importance of obedience to God. In studying this lesson I find myself wrestling with the lust of the flesh, the lust of the eye and the pride of life. My prayer is that God will help me to overcome this sinful nature through the power of the holy ghost.
A better translation would be do not murder!