The reaction of Chinese social media users to a spate of recent violent attacks has exposed widespread discontent about the nation’s downturn, as economic pressures mount.

Shanghai police reported a stabbing Wednesday morning in one of the city’s metro stations, which — like other subway lines in major Chinese cities — has security checks at its entrances. The suspect was detained after injuring three people and the case is under investigation, police said in a statement.

In a country where violence is relatively rare, the incident became a top trending item on social media platform Weibo, garnering some 164 million reads with users speculating on the attacker’s motive. Some suggested the culprit was a stocks investor, a group battered during China’s $7 trillion market meltdown earlier this year.