On July 21, a gang wearing white T-shirts and armed with poles and sticks set upon anti-government protesters -- unarmed and dressed in black -- at a metro station in Yuen Long, close to the Chinese border.
The attack left nearly 50 people in hospital -- including passers-by -- some with horrific wounds.
Hong Kong's police were heavily criticised for being slow to respond, fuelling rumours of collusion.
Police denied any links to the attack, but trust in the force -- which was already facing an unprecedented challenge on the streets -- has since sunk to a nadir.
As commuters returned home on Wednesday, protesters sat along the concourse at Yuen Long station, some holding placards saying "Free Hong Kong" and calling for the attackers to be brought to justice.
"People are here to tell the government that we are angry and we think that we need a fair judgment on the attackers," 23-year-old tutor Chloe told AFP, giving one name like many of the demonstrators.
Wednesday's sit-in was peaceful with most of the protesters seemingly not equipped for violent clashes with police -- unlike the frontline "braves" as the more radical protesters are known.
Hong Kong's political crisis was spurred by an attempt to bundle through a bill allowing extradition to China through parliament.
But protests have billowed out into a wider pro-democracy movement, which has seen the financial centre's airport closed, violent street clashes with police and million-strong peaceful marches through city streets.
The city has enjoyed several peaceful protests recently -- without police baton charges, tear gas or protesters hurling rocks.
It is unclear in which direction the protests, which are leaderless and organised on social media, are heading after nearly three months of draining street action.
Hong Kong's government has so far refused to buck to any of their demands, including scrapping the extradition bill completely, the resignation of city leader Carrie Lam and a full independent inquiry into police actions during the protests.
But they say they are digging in for the long haul.
"Although we are so tired, we know that the momentum for the protests is still there," said a sit-in participant who identified himself only as Leung.
Hong Kong police on Tuesday said they had arrested 28 people over the July 21 incident.
Yuen Long is in Hong Kong's New Territories, a rural area where many of the surrounding villages are known for triad connections and their staunch support for the pro-Beijing establishment.