I'm having problems with the Diplomatic Plasmatic Immunity Quest .

I'm at the last part where I free the prisoner guy. Went to the trap door saw that I need a key to open it. I went looking for the key and then kill the 2 guards that were holding that one guy hostage that help get me into the party in the beginning of the mission ,but when I check the guards body there was no trap key. I went looking for that key everywhere, but came to realize after watching a YouTube video the trap key was suppose to be on those two guards that was holding that one guy hostage. I reload the game a few times and try the scene again with no luck. Sometime I get no key and other times I would get the wrong key* . I went a couple save back starting the quest all over again hoping that it will work, I did on another quest and it did work, but sadly it didn't work this time. I can't contiune the main quest without this bug being fix.