The two images below are when Nahid leans on the door and the suddenly Jakir comes across, as we're seeing him from glass door we can't really Jakir but we can see his figure, this comes out as a mystery as it traps the audience in sense of suspense and eagerness to know who it is.
Nahid (victim) leaning on the glass door and Jakir (killer) comes behind him.
Here you can see Jakir (killer)
The four images below are when Nahid sees Jakir, and then suddenly he drops his glass, after dropping the glass it shatters in to pieces and the suddenly Nahids on the floor with blood coming out his mouth/head. It's a mystery what happened to the victim.
Nahid sees Jakir for the first time.
Glass drops from the victims hand.
Victims on the floor with blood coming out his mouth/head.