“What are you thinking about, Song Yang?” wondered Xiaotao.

“Before I tell you, I’ve got a little test for you,” I said. “How many types of serial killers are there?”

“Well,” Xiaotao thought about it for a while and answered, “There are sociopathic serial killers who are obsessed with power and control; psychotic killers who are compelled to kill by the voices in their head; missionary serial killers who believe it is their religious or social duty to kill a certain demographic; and the hedonistic serial killers who are driven by lust and thrill.”

These were the standard classification of serial killers, but they only dealt with their motivations. 

“Serial killers generally have their own clear style and targets,” I stated. “The victims all wore a red dress, they were all disfigured, and they were all hit on the back of their head....