Hong Kong police announced Tuesday they had arrested six men, some with ties to triad criminal syndicates, for involvement in a brutal mob attack on pro-democracy protesters Sunday.

The accused are thought to be behind gangs of thugs who used bamboo sticks and metal bars to pummel anyone suspected of partaking in protests against the government.

Videos published by eyewitnesses showed men and women dressed in white and covering their faces with surgical masks surrounding and beating individuals dressed in black, the color the pro-democracy movement has adopted, in Yuen Long, a town in Hong Kong’s New Territories north of the city center. Authorities confirmed on Monday that the mob’s attacks resulted in 45 people being hospitalized, one in critical condition.

Protesters say police allowed the attack to happen and calls to the city’s emergency hotline, 999, were met with apathy. Video circulated on social media of some of the white-clad thugs casually chatting with police officers, giving the impression that law enforcement officials approved of the violent spectacle.

Pro-democracy lawmakers and protest leaders denounced the attackers as members of triads, organized crime groups that have traditionally operated in Hong Kong. Police officials confirmed that claim in announcing the arrests of six men aged 24 to 54 for their participation in the mob attack.

Eyewitnesses told local media they believe hundreds of people participated in the mob attack. Law enforcement authorities estimated the mob to total around 100 people.

According to the Hong Kong Free Press (HKFP), a spokesman for the police confirmed that, among those arrested, “several had triad backgrounds” and that police are continuing to search for members of the mob, expecting more arrests to follow. The Hong Kong-based South China Morning Post identified the 14K and Wo Shing Wo triads as those suspected to have participated in the attack. The 14k triad, founded in 1945, is believed to boast as many as 20,000 members. Wo Shing Wo is believed to be the oldest triad in Hong Kong, established in 1930, and among the most violent.

Hong Kong’s triads have endured for decades through drug trafficking and other criminal activity. They thrived for decades in the Kowloon Walled City, a sprawling ad-hoc complex of buildings built upon buildings where police largely refused to enter until its destruction in 1993, allowing the triads to operate with little interruption. Triads survived the fall of the Kowloon Walled City in a much weaker state than they once were. Hong Kong police arrested the suspected head of Wo Shing Wo in 2017.

The Post called Sunday night’s attack in Yuen Long a “shockingly violent rampage of unprecedented lawlessness,” nothing that among the mob’s victims were at least one elected lawmaker and a pregnant woman. The mob circled the Yuen Long mass transit station to trap protesters seeking to take the train home after an anti-China protest ended peacefully, then began beating into the crowd with sticks and metal rods. Not all of those suffering injuries are believed to be protesters; many were passersby mistaken for being part of the march that had ended that day.

Protesters have adopted black as their color, but the Post notes that many have begun to organize and bring clothing of other colors to wear after the protest ends so that, in the event of another mob attack, they do not become targets.

Following the attacks, local reports indicated that many shopkeepers and businesspeople in Yuen Long feared opening again. Some businesses opened on Monday, but many closed early, as did some government facilities. Many in the area said they feared opening because they did not believe police would help in the event of a mob attack on them.

“Those men in white T-shirts beat people everywhere and no one was stopping them at all,” a restaurant owner in Yuen Long told the Morning Post.

“They only put on a show and arrested a few people last night. Where were they on the night the attacks happened?” a shop manager at Yoho Mall, where the transit stop the mob raided is located, told the newspaper., stating he would open his book shop temporarily but not risk remaining open if crowds begin to grow.

A coalition of pro-democracy lawmakers expressed similar concerns about the lack of police activity in response to Sunday’s mob attacks. A group of 24 legislators accused police of being “servants of triads” and declared they had “completely lost the public’s trust.”

“Last night, the 999 reporting hotline would not connect for a long time and the police station was closed. There were even police officers who pretended they didn’t see the actions of those in white shirts and red ribbons, and turned around to leave,” the lawmakers wrote on Monday.

Protests erupted in Hong Kong in June in response to pro-China lawmakers introducing a bill in the Legislative Council (LegCo) that would have allowed China to extradite any individual present in Hong Kong if accused of a crime according to Chinese law. Under the “One Country, Two Systems” policy, Hong Kong is technically a part of sovereign China but is run by its own laws, which respect Western civil and human rights norms. The law would have allowed Chinese Communist Party restrictions on expression and faith to override Hong Kong law, a violation of “One Country, Two Systems,” the protesters say.

LegCo tabled the bill in response to protests, which prohibits an immediate vote but allows lawmakers to revive the bill at any time. Protesters have continued taking the streets calling for a full withdrawal of the bill, which would eliminate it from consideration.

The ruling Communist Party of China has sternly condemned protesters, calling them violent and their continued acts of disapproval “absolutely intolerable.” Highest on the list of acts Beijing has condemned is the storming of the LegCo building, which, while peaceful, resulted in tremendous property damage and rendered it impossible for lawmakers to meet and conduct business for months. The protesters did not vandalize any property not directly related to lawmaking and ensured the protection of historical artifacts.

On Sunday, protesters vandalized the outside decor of China’s top liaison office in Hong Kong, the event that trigged the condemnation of the protests as “absolutely intolerable.” On Monday, the Chinese Communist Party propaganda outlet Global Times accused the people of Hong Kong of no longer respecting the rule of law and called for “lifting all the restrictions and harassment on law enforcement.”

“An essential cause of Hong Kong’s chaos lies in the greatly limited police power,” the newspaper contended. “Police must only recognize law, not political correctness. People who violate the law must be dealt with, regardless of their political pursuit.”

China’s state media outlets have not mentioned the Yuen Long mob attack at press time.

A reporter asked Chinese Foreign Ministry spokesman Geng Shuang about the mob attacks on Monday. Geng condemned the protesters, not the violent suspected triad gangsters for their behavior.

“I’d like to reiterate that the behaviors of some radical protesters have crossed the bottom line of the ‘one country, two systems’ principle. This is intolerable,” Geng said. “We firmly support the [Hong Kong] government in taking all necessary measures according to law to ensure the safety of central government institutions in Hong Kong, uphold the rule of law in Hong Kong and punish the criminals.”

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