“I am interested in crimes and why people commit crimes. While movies often depict intentional killings like premeditated murders, such crimes constitute less than 10 per cent of overall murder cases. Most murders in real life are committed by impetuous perpetrators who kill spouses and friends [in a rage].”

The title of the book refers to a dark universe on the internet hidden from the general public.

“The topic of the deep web hasn’t caught on in Chinese society. But it’s a popular topic in Japan, Korea, Europe and America. Even US TV series House of Cards mentioned it. I stumbled upon it after reading overseas forums. People on the deep web use pseudonyms. While ordinary people use browsers like Firefox and Internet Explorer, deep web users have to download a browser called Tor [for anonymous communication].

“The marketplace on the deep web is like an illegal version of Taobao where people can get child prostitutes and other illegal stuff using bitcoin [for payments].”

His books chronicle his forays into the deep web in which he tracked down anonymous criminals and had conversations with them.

“Some of them didn’t mind talking to me, as I am too far away from them. They just talked about their crimes and wouldn’t mention their location. For example, I have chatted with a filmmaker who made films of people fighting animals.”

It was shocking material like this that alarmed parents – the book was hugely popular with students in Hong Kong.

The first volume has been reprinted five times since its publication in May last year, and has sold some 10,000 copies. It was the eighth-best-selling Chinese-language book last year at Taiwan-based book chain Eslite.

Complaints by parents about the book first appeared on Facebook and in May, Deep Web was rated indecent by Hong Kong’s Obscene Articles Tribunal.

This means that, although they may still be sold in Hong Kong, the books must be wrapped with a notice to warn against their sale to individuals under the age of 18.

“However, after the incident, no major bookstores sell it,” Li says. “The books are only sold in small bookstores and on Taobao now.”

While parents panned him for corrupting the minds of young readers, Li – who goes by the pen name Scary Bird – says his writings go further than a mere voyeuristic fascination with crime and the dark side of human nature.

“There are psychological and sociological reasons for crimes that can be studied. Figuring out how crimes are committed takes logical reasoning and analysis. There’s a crime scene. There’s the psychological profile of a criminal to flesh out so that you know whether he committed a premeditated crime or did it on impulse. I like figuring all these out like a detective.”