I finally got it this afternoon. Took me about eight tries or so to get it, but it took me over two hours last night of just trying over and over again to the point of frustration too immense to continue playing.
Personally, I killed the guy in the washroom and ran up to shoot the guy in the doorway and took the left path. Other than that I just followed the same strategies and paths as the guys on YouTube. The only way to finish this mission is to get lucky. That's all I've found out.