*SPOILERS* Some unanswered questions..
1) Is his mother controlling his memories with acupuncture?
2) Did the mother permanently damage Do-Joon's brain by giving his pesticide when he was 5 y.o.?
3) Koreans have some pretty lame forensics, if they found out the cause of death for the girl, but couldn't for the junk collector. Even though he died in fire, he would have had skull fractures.
4) Did his friend Tae something help him put her on the roof? Sounded like he knew it was for "revenge" , and the junk collector recalled Do-Joon trying to call someone and flipping his cell phone after he killed Ah-Jung ?
5) Who is Do-Joon's father? Did his mother kill him too? Did he leave them and then she tried to kill herself and Do-Joon?
6)Where did she go at the end? By bus? Vacation?