He identifies one of the pictures on Ah - jung 's phone ; that of a white - haired elderly man .
In his cell , Do - joon remembers seeing a man in the building the night of Ah - jung 's death .
Do - joon identifies one of the pictures on Ah - jung 's phone ; that of a white - haired elderly man .
In his cell , Do - joon remembers seeing a man in the building the night of Ah - jung 's death .