Both Su Zheng and the middle-aged man could confirm from the picture that the person who broke into the safe was not that skillful. This meant that the chance of them being in the same circuit was low. For example, even though Su Zheng and the middle-aged man did not come from the same city, they would have heard of each other from other colleagues. Those in the same circle would be relatively familiar with one another, and each of them had their own specialties because they would not have come out to 'work' with half-assed skill.
If they were not in the same circuit, then this was most likely an amateur, those who had learned a thing or two and decided to earn money the illegal way, instead of doing actual business. Or perhaps they had family in the same business, so they were more familiar with safes than normal people.
