How do I earn the Pacifist Achievement?

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?

An unofficial, but popular Deus Ex wiki says the following:

"The aim is to complete the game without killing anyone directly, or someone dying as a result of an action taken by the player. The only exception to this is the Boss fights...killing anyone in the Prologue chapter will lock out this achievement

And currently, it appears there is no way to see if you are still eligible for the achievement at any time:

"Unfortunately if you lock out the achievement by accident, unless you aware that you did so and reload an old save, there is no indication that you have done so and may end up playing through the game and not get the achievement due killing a character earlier in the game."

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.

Actions which disqualify you for the Pacifist achievement:

• Killing a non-boss character directly (shooting them, lethal take down)
• Killing someone through a hacked turret or robot
• Killing anyone in the opening sequence of the game

Actions which will not disqualify you for the Pacifist achievement:

• Using an EMP on a robot
• Neutralizing an enemy through non-lethal means (stun gun, non-lethal take down, et cetear)

It should also be pointed out that it is possible to defeat the final boss through non-lethal means, so using lethal means could also result in losing the Pacifist achievement. This answer covers how to do that.