If I remember correctly (and my memory is a little hazy at this point), the vial should be
SPOILER:
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on one of the guards that you killed in the entrance of the place. Try holding down the tab key so all the items on the ground are highlighted.
I'm not 100% sure that's where it is, mind you. Anyone around with a better memory then me?
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"Our deepest fear is not that we are inadequate.
Our deepest fear is that we are powerful beyond measure."