This is my theory about the 'Haiya massacre case'.
In the trailers, they mentioned the 'Jifeng Pill', which seemingly caused people to turn into crazed beings. Bei Hai, a disciple of the Poison Valley, may have created this pill under Wu Lie's orders to heighten the military prowess of the Cangfeng army. However, things went downhill when they tested on the soldiers. It seems that to prevent the infected from reaching further inland, to the capital, the massacre had to take place. Their greed dragged the Haiya people into this tragedy. Bei Ming and his older brother were entrusted to Zhong Yun Chi (Xue Man's father) like that. Like others have mentioned, Bei Kun, the brother, is most likely the main culprit, Yesha.