Pro-democracy protesters hold a placard with Chinese words "Collusion of police and triad" to mark the anniversary of the attack by more than 100 white-wearing men with pipes and poles on July 21 last year, at Yuen Long, in Hong Kong, China July 19, 2020. REUTERS/Tyrone Siu

Protesters stand inside at the Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China, August 21, 2019. REUTERS/Ann Wang

Protesters stand inside at the Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Ann Wang

Protesters stand inside at the Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Ann Wang

Protesters look out from a train car at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Ann Wang

Protesters look out from a train car at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Ann Wang

Protesters stand around a fare gate inside Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Ann Wang?

Protesters stand around a fare gate inside Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Ann Wang

Protesters climb an escalator inside Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Ann Wang

A protester holds a sign inside Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Ann Wang

Protesters beat the ceiling as they face riot police during a stand off at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Tyrone Siu

Protesters stop the door of a Mass Transit Railway (MTR) subway from closing to allow more protesters to board the train to retreat during a rally at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Tyrone Siu

Protesters stop the door of a Mass Transit Railway (MTR) subway from closing to allow more protesters to board the train to retreat during a rally at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Tyrone Siu

Protesters face riot police during a stand off at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Tyrone Siu

Protesters stop the door of a Mass Transit Railway (MTR) subway from closing to allow more protesters to board the train to retreat during a rally at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Tyrone Siu

Protesters face riot police during a stand off at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Tyrone Siu

Protesters face riot police during a stand off at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Tyrone Siu

Protesters face riot police during a stand off at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Tyrone Siu

Protesters face riot police during a stand off at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Tyrone Siu

Protesters face riot police during a stand off at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Tyrone Siu

Protesters stop the door of a Mass Transit Railway train at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Ann Wang

Protesters face riot police during a stand off at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Tyrone Siu

Protesters face riot police during a stand off at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Tyrone Siu

Medics help a protester at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Ann Wang

A protester gestures at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Ann Wang

Police members are seen as people protest at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Kai Pfaffenbach

Medics help a protester at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Ann Wang

Riot police members check the bag of a man at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Ann Wang

Police members are seen as people protest at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Kai Pfaffenbach

Riot police arrest a man at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Ann Wang

A woman walks past protesters in Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Ann Wang

An anti-extradition bill protester uses a hose as he faces riot police during a stand off at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Tyrone Siu

People protest during a silent sit-in gathering at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Ann Wang

People protest during a silent sit-in gathering at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Ann Wang

People protest toward the riot police at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Ann Wang

Riot police asking the media to move at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Ann Wang

Anti-Extradition bill protesters face riot police during a stand off at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Tyrone Siu

Protesters walk inside a mall at Yuen Long MTR station after a stand-off with police at the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. Picture taken August 21, 2019. REUTERS/Thomas Peter

Protesters stand inside Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Ann Wang

Protesters face riot police during a stand off at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Kai Pfaffenbach

Protesters face riot police during a stand off at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Kai Pfaffenbach

Protesters walk inside a mall at Yuen Long MTR station after a stand-off with police at the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. Picture taken August 21, 2019. REUTERS/Thomas Peter

Protesters build a barricade inside Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. Picture taken August 21, 2019. REUTERS/Thomas Peter

Protesters walk inside a mall at Yuen Long MTR station after a stand-off with police at the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. Picture taken August 21, 2019. REUTERS/Thomas Peter

Protesters build a barricade inside Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. Picture taken August 21, 2019. REUTERS/Thomas Peter

Protesters build a barricade inside Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. Picture taken August 21, 2019. REUTERS/Thomas Peter

People protest during a silent sit-in gathering at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China, August 21, 2019. REUTERS/Willy Kurniawan

Protesters sit in Yuen Long MTR station after a stand-off with police at the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. Picture taken August 21, 2019. REUTERS/Thomas Peter

Protesters build a barricade inside Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. Picture taken August 21, 2019. REUTERS/Thomas Peter

A protester pushes a wheelchair to build a barricade inside Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. Picture taken August 21, 2019. REUTERS/Thomas Peter

People walk inside Yuen Long MTR station after a stand-off with police at the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. Picture taken August 21, 2019. REUTERS/Thomas Peter

Protesters face riot police during a stand off at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. REUTERS/Kai Pfaffenbach

Protesters stand behind fire extinguisher as they face police inside Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. Picture taken August 21, 2019. REUTERS/Thomas Peter

Protesters face riot police during a stand off at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China, August 21, 2019. REUTERS/Willy Kurniawan

Protesters retreat from police outside Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. Picture taken August 21, 2019. REUTERS/Thomas Peter

People watch police advance as protesters hide inside Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. Picture taken August 21, 2019. REUTERS/Thomas Peter

Journalists take pictures of a protester using a fire extinguisher inside Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. Picture taken August 21, 2019. REUTERS/Thomas Peter

People protest during a silent sit-in gathering at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China, August 21, 2019. REUTERS/Willy Kurniawan

Protester prepares during a silent sit-in gathering at Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China, August 21, 2019. REUTERS/Willy Kurniawan

A protester watches police outside Yuen Long MTR station, the scene of an attack by suspected triad gang members a month ago, in Yuen Long, New Territories, Hong Kong, China August 21, 2019. Picture taken August 21, 2019. REUTERS/Thomas Peter