I found quite a simple way of getting this:
Expedition- Mode: Score Attack/Replay Chapters Elite, Level: The Acropolis, Difficulty: Doesn't matter but I did it on Adventurer.
At the start activate the cutscene, then stealthy make your way back to the steps. Aim at the guy on the rights head (I used the bow).
For some reason the achievement didn't pop in the video, not sure why any problems leave a comment:
Sorry, this Game Clip has been removed