Heng Sao Tian Ya
If I remember correctly he not only used Sun Qiang's name, but also appearance. It would not be surprising if King Zhongqing, a suspected poison master, had heard about the whole situation. I don't know exactly what beef he has with him though. Perhaps a person he knows was killed when Zhang Xuan visited or maybe he was trying to get Sun Qiang's knowledge since the matter involving the founder was probably not revealed.