Please dont read if you jave not watched the movie.
The climax can be interpreted in two different ways.
1. A plain straight forward interpretation
Ben can be understood as a sociopath killer who kills women who thinks freely , he calls then green house. Jong su understands it and take revenge on him for killing hae mi. There are many clues pointing towards this interpretation.
a. Ben says he has found next green house and its close to jong su
b. jong su confirms that no physical green house is burned near his home.
c. Ben says he is bot working but playing.
d. Hae mis watch is found in Bens collection of women accesories
e. Presence of Cat named boiler at Bens house
f. Last call from Hae mi to Jong su were he could here panting and sound of running.
g. Hae Mis room is arranged perfectly which is the character of Ben and not Hae mi.
2. Different interpretation
Jong su is seen writing his novel before climax and the climax scene which comes after the scene may be what he writes in his novel and Ben actually may be a gentleman and Hae Mi might have just moved on to find the great hunger and meaning to her life.
Scenes pointing to this climax.
a. Ben has many friends and he is treated as a gentleman by all and there is no scene in this movie pointing towards other side on Ben.
b. Before climax Jong Su is shown of writing his novel and scene cuts into Bens house.
c. Hae mi on multiple occasions have told that she just wanted to disappear and she is afraid of death also.
d. Hae Mi is shown as an unrwliable person were on multiple occasions she has created fictional stories and narrated it as real like the case of well which she fell during childhood which jong su cant even remember.