I wouldn't apply murder to Legion. Legion is a being not necessarily constrained by organic attitudes and logic. Miranda has likely killed in the line of her duty (as well as killing a defenseless Wilson in cold-blood), but whether or not you believe that constitutes murder is up to how you define murder. I believe Kasumi has killed (what would you call the Hock job)?
A heist. She and Shepard took down a gunship pouring fire in their direction.
Now, with the guards in the security station towards the start of the mission, you may have a point. I try to knock those guys out before she can gun them down.
I don't buy the "Legion didn't think it was murder, so it wasn't" line of argument. Likewise, the Morning War-era Quarians thought they were decommissioning malfunctioning machines - their perception doesn't change the fact that they weren't, and that it was genocide. Batarians may see slavery as no big deal, that doesn't mean we're compelled to concede to their perspective when they raid human colonies.