The person's footsteps were light and slow; if Yan Junze had been fully focused on the female corpse, he might have easily overlooked the sound.
If it hadn't been for the screech of the door opening above, it's likely that the other person could have descended to the basement and walked up behind Yan Junze without him noticing.
Fortunately, the sound of the door alerted him. Yan Junze, huddled in a corner of the basement, had turned off his phone's flashlight, and was now engulfed in darkness, unable to even see the steps at the entrance of the basement.
A faint light filtered from the room above, so he could only vaguely make out the approximate location above the entrance.
Just then, a dark figure blocked the last bit of light seeping in and slowly descended the stairs.
The person moved very slowly, as if carrying a thousand pounds, with footsteps that sounded like they were dragging along the ground.