The true killer is him *spoiler.... obviously*

I wonder if anyone share similar opinion with me

the definite clues were :

1. the culprit's hands are smooth like a girl
field workers are automatically out, including factory workers and mechanics

2. no pubic hairs were found
no matter how careful someone, cleaning up after rape mess in a rainy night is impossible to recover all pubic hairs, meaning that the stupid cop's deduction was right that he is hairless down there, but we have no way to check so it's useless

3. the culprit managed to always find pretty girl alone in the dark rainy night
is doing something like that easy? well the first 3 victims wore read, it's true that red stand out in the dark, but to always find delicious targets means that he is a local who knows villager's habit, the rest of the victims ain't wearing red to boot

4. retard's confession that saying the culprit threw him into fire when they were little also supports the notion that the culprit is local

5. the final scene which took place 17 years later, the girl said to the ex-detective that the man who supposedly culprit is plain, ordinary. This means that during the incidents 17 years ago, the man was quite young that after 17 years he can still be called ordinary, instead of old, this killed the possibility that the culprit is the pervert who jerked off to underwears

so.... based on that.. I announce the true killer is!!!!!!

the guy in the pharmacy
he was shown as the last person who encountered the supposed to be the last victim (the stupid detective's girlfriend) before the culprit switch target to the schoolgirl

considering his work, his hands most likely smooth, he is a local and quite young. How someone can find his intended target in a dark rainy night? it's easy if they were customers of your store, you just have to stalk them after they leave from your store as in the case of the idiot detective's girlfriend

about the DNA, it might've been his or someone else's planted by him, by his line of work there's many ways to obtain semen

as for why park hyun-gyu the main suspect is not the true killer is simply because I don't believe a culprit is someone who wrote his name and address in a letter which may as well be anonymous, they're just letters to request song, just put random name and address there if he were the true killer