There have been some extended discussions on what will or will not break your eligibility for the Pacifist achievement, but nothing conclusive as to what actually is taken into account.
What actions (either directly or indirectly) result in an ineligibility to earn the pacifist achievement?
Additionally, is there any way to check one's save game to see if they are still eligible for the achievement?
Best Answer
An unofficial, but popular Deus Ex wiki says the following:
And currently, it appears there is no way to see if you are still eligible for the achievement at any time:
This seems to be a fairly sought after feature though. Since the game has been so popular since its release (over two million units sold already), I would not be surprised if a patch is released soon resolving these complaints.