SPOILER SPOILER SPOILER
The movie's central theme is not the identification of the killer. That would make it a normal police procedural. The theme is the detective's evolution to an understanding that as much as we might wish for certainty and resolution, sometimes those are unobtainable and we have to learn to deal with that horrible unknowing.
At the beginning of the film, he is so certain of everything. He can tell who did a crime just by looking in their eyes. He knows he has the right killer. Going through the procedural steps is a mere formality to be dispensed with by whatever means are necessary. You need evidence to back up what you know? Plant the footprint. You need a confession to confirm what you already know? Beat it out of your suspect, using doses of sleep deprivation and isolation to help.
When the Seoul detective disputes his conclusions, it makes him violently angry. You don't challenge certainty! That is like someone telling you your religion is wrong because certain evidence is lacking. Belief is sufficient to itself!
But as things progress, he loses faith in the certainty of certainty. They think they have an eyewitness in the young mentally challenged boy. But before they can get their absolute confirmation, the boy is killed, senselessly. The detective tries his "look into my eyes" trick on the suspected killer by the tunnel and realizes that he can't tell anything by looking at him. All that is left is the doubt and uncertainty that the Seoul detective now cannot cope with. The two men have changed places in the narrative.
I don't know if you read the letter that comes back from the FBI (it is shown very briefly). But importantly, it does not say "You have the wrong man... The DNA exonerates him." Instead it says "Results are inconclusive. We are unable to confirm that the two DNA samples are identical." So the Seoul detective doesn't break down because of conflicting evidence, it's the terrible lack of conclusive resolution that he had been desperate for... relying on it to give him the justification he needed to put the killer away.
The final scene is powerful because after all these years, the ex-detective happens upon an eyewitness who obviously saw the killer back at the scene of the crime. All she needs to do is give him something concrete that he can use to confirm or deny that their man was actually the killer all those years ago. He allows himself to hope that finally he will have the external evidence he needs to tell him whether he was right or wrong.
And all the girl can say is that the man looked "ordinary." What a perfect description of the actor they had playing the suspect! Can you think of any distinguishing physical characteristics that would define him? And it leaves the ex-detective with the same dashed hope of resolution and certainty. It tells him nothing. That could describe his suspect and could describe anyone else. He looks into the camera and we see his pain and frustration that once again, the answer is unknowable. And by looking us directly in the eyes, it makes us confront the same fact... You think you are going to get a nice tidy wrap up of who the killer was in this little thriller movie? Sorry... Prepare to live with the frustration. Some things in life are unknowable. Can you live with the uncertainty? How do YOU cope?
It left me feeling unrewarded and a little angry at the end of the film as well. I'm used to resolutions in my movie mysteries. But then I thought about it more and saw how powerful this message is.
