Now that we know Liu Wei is the murderer, the investigation of this case becomes much simpler.
Luo Fei first called Wu Yan, telling her that he had things to do tonight and wouldn't be coming home immediately. He might return very late, so they shouldn't wait for him.
Afterwards, Luo Fei went directly to the police station to check the surveillance at the intersection of Huang Guang Lamp from last night.
This is a necessary route from Peach blossom Village and Shi Family Village to the county town. If Liu Wei is indeed the murderer, his trail should be found on the surveillance footage.
Sure enough, in no time, Luo Fei found Liu Wei's figure in the footage.
