Why did Lei Yang, a 29-year-old man, try so hard to escape from police, which ultimately cost him his life, when he was being escorted to a Beijing police station on an alleged prostitution charge?

Because he knew the price he needed to pay was far more than the 200 yuan he gave the sex worker - possibly a 5,000 yuan ($768) fine, and a maximum of two years detention at the discretion of police.

China in 2013 abolished re-education through labor, a punishment that allows police to detain people for up to four years without an open trial. But a similar detention system for those involved in the sex trade enacted in 1999 still applies, which also allows police to detain an untried citizen from six months to two years.

Separately, some local police stations have assigned a quota to officers to collect a certain amount of money as part of their work. Wu Youming, a retired police officer, wrote in a book that every officer in his team needed to bring in 1,500 yuan in fines from sex workers and their clients every month.

However, police sometimes fail to issue a receipt for the fine, and the john might be fined multiple times by different police officers as he could not prove he has already paid the fine for his crime, noted Wu. In an extreme case, a john was fined three times, 5,000 yuan each time.

If the sex trade was not punished this harshly, Lei would not have tried so desperately to escape, and he might not have died over such a minor offence. In addition, such punishments have not prevented or reduced the sex trade, but made the industry into an unregulated area that breeds corruption and other crimes.

The best way to address the problems in this unregulated industry is to decriminalize sex work that is conducted voluntarily between adults, with or without money involved.

The author is Li Yinhe, a sexologist with the Chinese Academy of Social Sciences