A man reacts to the effects of pepper spray during an event 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.

Riot police stand guard during a protest to mark the first anniversary of an attack in a train station by an armed crowd wearing white shirts, demanding justice for the victims of violence and broader freedoms, at a shopping mall in Hong Kong's Yuen Long, China July 21, 2020.

Pro-democracy demonstrators dress in white and hold sticks on their hands to mock an incident took place one year ago which armed crowd wearing white shirts attack passengers train station, during a protest to mark the first anniversary of the attack, demanding justice for the victims of violence and broader freedoms, at a shopping mall in Hong Kong's Yuen Long, China July 21, 2020.

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. Image used for illustrative purpose

"HK Add Oil" stickers are seen next to a riot police during a protest to mark the first anniversary of an attack in a train station by an armed crowd wearing white shirts, demanding justice for the victims of violence and broader freedoms, at a shopping mall in Hong Kong's Yuen Long, China July 21, 2020.

Pro-democracy protesters march 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.

A man (L) is searched by Hong Kong police Special Tactical Squad during a protest to mark the first anniversary of an attack in a train station by an armed crowd wearing white shirts, demanding justice for the victims of violence and broader freedoms, at a shopping mall in Hong Kong's Yuen Long, China July 21, 2020.

Riot police stop and search people during a protest to mark the first anniversary of an attack in a train station by an armed crowd wearing white shirts, demanding justice for the victims of violence and broader freedoms, at a shopping mall in Hong Kong's Yuen Long, China July 21, 2020.

Pro-democracy activists Eddie Chu Hoi-dick and Gwyneth Ho Kwai-lam hold papers with Chinese words "No police turned up on July 21st" 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.

Police take away a protester to avoid people to gather 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.

A man is searched by Hong Kong police Special Tactical Squad during a protest to mark the first anniversary of an attack in a train station by an armed crowd wearing white shirts, demanding justice for the victims of violence and broader freedoms, at a shopping mall in Hong Kong's Yuen Long, China July 21, 2020.

Police disperse pro-democracy protesters with pepper spray as they gather 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.

A pro-democracy demonstrator holds a paper with a symbol of "Five demands, not one less" during a protest to mark the first anniversary of an attack in a train station by an armed crowd wearing white shirts, demanding justice for the victims of violence and broader freedoms, at a shopping mall in Hong Kong's Yuen Long, China July 21, 2020.

Pro-democracy protesters march 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.

Riot police ask people to leave to avoid mass gathering during a protest to mark the first anniversary of an attack in a train station by an armed crowd wearing white shirts, demanding justice for the victims of violence and broader freedoms, at a shopping mall in Hong Kong's Yuen Long, China July 21, 2020.

Riot police ask people to leave to avoid mass gathering during a protest to mark the first anniversary of an attack in a train station by an armed crowd wearing white shirts, demanding justice for the victims of violence and broader freedoms, at a shopping mall in Hong Kong's Yuen Long, China July 21, 2020.

A police officer holds a pepper spray to disperse pro-democracy protesters gathering 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.

Pro-democracy demonstrators are searched by riot police during a protest to mark the first anniversary of an attack in a train station by an armed crowd wearing white shirts, demanding justice for the victims of violence and broader freedoms, at a shopping mall in Hong Kong's Yuen Long, China July 21, 2020.