There were many signs which pointed to the presence of a traitor within Kun Society, and furthermore that he or she was of an important position.
Gu Shenwei had already reached this conclusion after Shangguan Ru was abducted in the deserted village. The mole had to be very familiar with Tenth Young Master and Slave Huan to know that there was a great disparity in their Lightness Skills.
Subsequently, during the duel in Rouge Forest, the assailant apparently understood Slave Huan's tactics and waited patiently nearby.
Even fewer people knew about the campaign to assassinate the Machete God Huang Shi'an, yet the squad still fell into the enemy's trap. Had Gu Shenwei not called off the mission at the last possible moment, the casualties would perhaps not have been limited to one killer.
The first person whom Gu Shenwei suspected was Shangguan Yushi.