The many suspicious aspects surrounding Xu Yin could be easily pieced together to find the answer once his identity was exposed.
While waiting for the progress of the palace affairs outside the East Hua Gate, Fu Zhen had already thought it through. Based on her six years of interaction with Xu Yin, all the details could prove that her speculation about Xu Yin's faction was factual.
However, the matters involving the Crown Prince remain noteworthy when mixed in.
Xu Yin could hide well in Great Zhou using the remaining forces of the Prince Yi Mansion. But how did they know that the Crown Prince of Great Zhou had fallen outside? And why did they recognize the deceased's identity on the night the incident happened? Apart from them having had contact with the Crown Prince, Fu Zhen could think of no other possibility.
Of course, even if he had been in contact, it wouldn't mean much because the Crown Prince's fratricide had nothing to do with him.
