Why 5 victims? I understand that the granny was omitted because she wasn't chosen and it just turned out that…
The girl from the greenhouse is linked to the fairytale "The Fox and the Grapes", she was mentioned on the show. The boxer guy was the first victim, the killer wanted to take revenge on him and since it was his first kill it kinda triggered him.
You're right. Has this been confirmed anywhere in the drama? I don't recall it being confirmed.
At the start of ep 3, when Choi Hong Ju was at the hospital watching Song Soo Ho and Song Soo Jung's mother who tried to kill herself, sha had a flashback where she left the bag wih the boxing gloves Song Soo Jung had bought for her brother.
The boxer guy was the first victim, the killer wanted to take revenge on him and since it was his first kill it kinda triggered him.