He goes there and finds some news cuttings. The man also comes there and tries to run away. Finally he beats Kang severely. Later on, he comes back to the police station and faces Seong-ho, who gives him more riddles. Meanwhile, all these raise suspicion in Min's mind and when she proceeds to arrest Kang, Kang tells her the truth.
Kang was beaten up, he didn't have the chance to actually check everything in the house, when he was beaten up he had to go to the police station. I believe the man other man went there to mislead him from finding his daughter.
Now, to show Seong-ho as innocent, Kang tempers with the murder weapon. He removes the trace of blood from that and put his dog's blood. He also mislead Min to show Seong-ho as innocent. Next day, Kang meets Seong-ho again and asks him about the real murder weapon, so he can hide it from the police. But Seong-ho doesn't disclose that. He gives Kang some clues about his motives. Kang then beats Seong-ho. He goes to Seong-ho's house to find the weapon and the police also reach there for the same reason. He hides from the police. Later on, from the local police, he gets the address of the man who gave him his daughter's photos.
He goes to the house for this reason, because he got the address of the person he suspected knew about the real murder weapon (Seong-ho). His daughter's remains was always there-right from when Kang received the envelope at the air port.
Now, I am not sure what you mean by this, but I am fairly certain that you mean Is she dead before the first scene of the movie?
Think about it, when Kang received the photos in the envelope at the air port, they showed him his daughter didn't they? When he went to the police station to report it, it was evident something happened to his daughter and there was obviously a plot against him.
If he got the address for the house, they would have hidden the box containing his daughter, but they didn't and Kang went through the house not knowing she was in there, only to be attacked by the other man.
Also, why would Kang be given three days to free Seong-ho by Seong himself by tampering with the evidence so then he would spare Kang's daughter...why would they spare his daughter-it is clear right there that she is dead, they were never going to spare her in the first place.
Kang's daughter was dead right from the start when Kang received the envelope at the air port.