The one from the horse ride? For that you have to have seen the scene in the forbidden wink in that week but before the ride happens. I think you need a decently high quick wit stat for it
I'm referring to the assassin who tries to kill us in Week 5 and Week 6 right before the ball. (I know who is behind the horse right, but thank you anyway)
It's impossible to find out the identity of that assassin (right now) I think Aly mentioned that we'll be able to find out when playing the "Player of The Grand Game" secret background once it comes out.