My comment comes from my perspective as a combat veteran and former Marine. First of all let me say that there in no place in war for brutality, though I do advocate the use supreme force.
Secondly that the need to respond split second life and death situations can at times lead one to false conclusions. Example in the story being referenced (if one takes into consideration the time period spoken of) a taxi with 5 men pulled along side the Marines (how many taxis have been used to kill Marines and other military combatants?) perhaps a wrong decision was made that implicated the men in the taxi as terrorists and the statement is made 'TERRORISTS' at this point the entire fire power of the squad will be turned toward the perceived danger to the group. In the heat of battle whether perceived or real anyone who comes on the scene will be construed as enemy and fired on.
I am not saying this is right what I am saying is urban warfare is different than frontline warfare. Put yourself in those Marine's shoes, you are inside a city where many want to kill you, you cannot tell who is a terrorist and who is not, your reactionary senses are fully set.
Today much more is known of urban warfare, soldiers are taught with better techniques and with the help of computers reaction is taught to look for certain things.
Unfortunately mistakes happen, this does not make it murder. Can a Marine commit murder absolutely! Did these Marines commit murder probably not though in the aftermath it may have looked like murder in all probability this was a situational mistake of judgment.
Please do not judge combat decisions to be the same as seen on TV whereby the soldier has 10-15 seconds to respond. Death by bullet is literally a second away.