So at what point did you know? SPOILERS
I diddn't know anything about this movie before seeing it so I wasn't looking for a twist but some some things caught my attention.
1) When the tourist first gets attacked in the hotel bedroom the morning after the kiss he scales across some roof tops and balconies without any hesitation. While this diddn't give it away to me I thought it to be a bit strange for a teacher.
2) When the crime boss kingpin strangles one of his men, I got the feeling that it was pretty cliché and to not expect much in the way of intelligence form the movie.
3) I only guessed it was him when he excaped from the police at the end and the head police guy kept saying he will turn up.
So when did you guess it was him?