How?

In a building a few meters away, where the windows of the second floor offered a clear view of the warehouse's back door, Chen Youzhi crouched low in wait. He was to assist He Juan if – God forbid – something went haywire in the middle of the operation. 

This building was the perfect place for him to scout the situation because it was close to the warehouse – too close to set up an ambush though, so he did not have to fear the police coming here – and its low structure made it a less ideal location for the police to spy the situation inside, not when there were many taller buildings around, thus leaving this lone building all to himself. 

Or so Chen Youzhi had thought. 

After confirming with He Juan that he was ready in position, Chen Youzhi fixed his gaze on the warehouse, ready for any signal that beckoned at him. However, at that moment, his acute hearing detected the unmistakable sound of footsteps.