It always bothers me how John didn't immediately kill Hans the moment he realized it was him, but it's so awesome they meet unexpectedly at this point in the movie
It’s because John ain’t that serious. He cracks a lot of jokes throughout the movie. He didn’t know the guys would come up. He was just trolling Hans for fun.
It’s more a he very strongly suspects but his conscience won’t let him till he knows without a doubt. Cos killing an innocent man on a hunch is not the type of man he is.
Hans is hands down obviously the best die hard character and die hard villain. I love hans gruber and I think that Alan rickman nailed the performance.