Thousands of Hong Kong residents held a sit-in on Wednesday at the MTR railroad station in Yuen Long, where protesters were savagely attacked on July 21 by thugs linked to organized crime gangs. The demonstrators used the one-month anniversary of the attack to complain about the lack of an independent investigation of the Yuen Long incident and instances of excessive force used by the police against protesters.

The sit-in on Wednesday featured demonstrators holding placards that accused the police of failing to prosecute any of the “white shirt” thugs who stormed the MTR station in July and attacked passengers with clubs and poles. (The attackers wore white to distinguish themselves from the protesters, who favor black clothing.)

The demonstration started quietly but appears to have grown more rowdy as more protesters and police arrived.

“Police clashed with some protesters who sprayed fire hoses from the subway station. Others smeared the station floor with cooking oil to try to stop the police advancing,” Reuters reported.

The Yuen Long incident in July was a major milestone in the protest movement, as Hong Kongers were shocked that gangsters would be hired to physically assault them, and enraged that police and MTR officials appeared to either respond very slowly to the attack or actively facilitate it.

There have been 28 arrests over the incident to date, but no charges have been filed, although Hong Kong Justice Department officials have implied some prosecutions are coming soon, possibly for charges so minor they will further infuriate the protest movement.

“People are here to tell the government that we are angry and we think that we need a fair judgment on the attackers,” said one attendee of Wednesday’s sit-in.

“In Yuen Long, one month ago, Hong Kong citizens and passengers were attacked by triads, and I think we should continue to press the government to investigate what went wrong that night and stop similar incidents happening again,” said another.

Many of the demonstrators covered their right eyes – a visual reference to another watershed moment in the protests when a young woman whose eye was severely injured after police fired on protesters with non-lethal ammunition two weeks ago.

Hong Kong protesters are angry about the inconclusive police investigation of the incident, while critics of the protest movement have suggested the woman’s injury might have been caused by a projectile flung by another demonstrator rather than the police. The police blamed protesters for failing to heed warnings that non-lethal ammunition was about to be used against them.