In the early hours of Feb 9, two gunshots rang out in Mongkok.
A Hong Kong police officer fired twice into the air before pointing his gun at enraged protesters who were apparently advancing on a fallen officer. While most retreated, a group of about 10 stood their ground. "Open fire and kill us!" they taunted him.
The scene, witnessed by 17-year- old student Andrew Chan, who contributes to a citizen journalism website, indicated a game of brinksmanship that some protesters now seem prepared to play, he said.
Activist Max Chung, who was also present that night, added: "Protests are not about sitting around, singing karaoke - and then democracy will come." It was a clear swipe at the 2014 Occupy movement, which was admired for its largely peaceful ways but failed in its demands for greater freedoms to elect the city's leader.
Instead, argued the founder of a small "localist" group, Hong Kong Blue Righteous Revolt, "we have to step up. We have to increase the level of violence".
Major localist groupss
HONG KONG INDIGENOUS
The main group behind the chain of events leading to the riot was Hong Kong Indigenous.
On the first day of the Chinese New Year, it called on supporters to gather at Mongkok's Portland Street at 9pm that night, in support of illegal street hawkers ahead of an impending raid by the authorities.
As the unrest unfolded, the group continued to play a leading role. According to local media, members stopped cars from entering Portland Street. Later, it urged more people to join them at Mongkok and to bring along goggles, masks, water and protective clothes.
Almost half of the about 70 people arrested so far are from the group, including its spokesman Edward Leung.
Hong Kong Indigenous started last year with 40 members, mostly in their 20s. It now has about 50,000 followers on Facebook, and styles itself as an aggressive defender of Hong Kong culture, values and rights, if not a fighter for outright independence.
It grew out of the more radical fringe of the 2014 Occupy student-led movement that wanted to use more confrontational means.
When Occupy ended without securing concessions from Beijing, Hong Kong Indigenous was formed. It became known for organising rowdy protests against mainland tourists and parallel traders.
Its modus operandi, which includes the use of violence, stems from a belief that Hong Kong's pan-democrats and even the Occupy movement's use of relatively moderate and non-violent ways have failed in "safeguarding" Hong Kong under communist Chinese rule.
"We are a group of nameless Hong Kong people who are on the frontline of protests," it writes on its Facebook page. "Since the old resistance methods have failed against the authorities, we have no choice but to stand out and break the stalemate."
Founded by veteran social activist Wong Yeung Tat in 2012, Civic Passion is similarly driven by "localist" principles but stops short of calling for independence.
Its yellow-clad members are prominent in many of Hong Kong's protests, and are often at the forefront of scuffles with the police.
Its members, including Mr Wong, took part in the Mongkok riot and one was arrested. But it played no part in its organisation, Mr Wong tells The Straits Times. He said that he was motivated to take part in the protest after seeing footage of a police officer firing two warning shots. "It was absolutely unnecessary, and I felt the need to go down to protest against such police brutality," he said.
Best known for successfully spearheading a 2012 protest opposing national education curriculum and the 2014 Occupy movement, Scholarism seeks greater autonomy for Hong Kong while working within the existing system.
It is, for instance, forming a new political party to contest legislative council elections later this year.
One of its members, Oscar Lam, was nabbed for involvement in the Mongkok riot - a move that Scholarism called "indiscriminate arrest".
"If one or two protesters die, then it will be like Taiwan's 228," he added, referring to the Feb 28, 1947 incident where a dispute between a cigarette vendor and an enforcement officer ignited an uprising against the Kuomintang government and led to a bloody crackdown. The episode catalysed the formation of a Taiwanese identity separate from the Chinese.
"No one wants to see anyone die. But it's been 30 years since we have been asking for democracy, and this government does not want to talk. We have no hope and we are not scared of dying to bring about a normal Hong Kong."
Protests are not about sitting around, singing karaoke - and then democracy will come.
ACTIVIST MAX CHUNG, who was at Mongkok on the night of Feb 9
Much of such talk is perhaps just bravado. But what is clear is an increasing willingness by a segment of society to resort to brute, provocative force - in the belief that all other options are bankrupt. Thus the mob violence that flared up on the first day of the Chinese New Year, which was the worst conflict in Hong Kong since riots in the 1960s.
On one side, protesters prised bricks from pavements to hurl at the police, and set fire to bins and even a taxi. On the other, police officers unleashed pepper spray and rained down blows with batons. About 130 people were injured, more than half of whom were police officers.
While many, including top government leaders, panned the protesters' actions as simply hooliganism, some are looking deeper into underlying causes.
What happened was likely both organised and spontaneous, said sociologist Lau Siu Kai, vice-chairman of the Beijing-backed Chinese Association of Hong Kong and Macau Studies. While "localist" groups, most notably one called Hong Kong Indigenous, played a role in agitating the crowd, participants included passers-by in the busy district.
What drove them to partake in the violence is a sense of helplessness, said Professor Lau. "What we see now are radical youngsters frustrated with our system. They don't think they can effect change with moderate or peaceful means, and so they resort to violence."
Mainstream channels, such as the legislature, appear ineffectual. When the Occupy movement - massive as it was - also failed to produce positive outcomes, an escalation was deemed necessary.
Using violence could thus rouse society to acknowledge their grievances, said Prof Lau. By creating situations to provoke police "brutality", they also gain sympathy and support.
So what were they unhappy about? The defence of street hawkers was the ostensible reason. Hong Kong Indigenous had called for supporters to gather in defence of a long-standing festive tradition: illegal hawkers peddling their wares while the authorities turn a blind eye. But, it appeared, the food and health authorities were planning a crackdown that night.
This is in tandem with the fear that Hong Kong's culture and values are under threat by China - whether it is the flood of Chinese tourists, lack of freedoms to elect the chief executive or the disappearance of Hong Kong booksellers.
Unhappiness over bread-and-butter issues - rising social inequities and the lack of upward social mobility - added to the tinderbox. About 40 per cent of the about 70 people arrested are unemployed, estimated journalism academic Francis Lee.
A fundamental issue is the lack of hope among the young and absence of trust in the government, including the police, to defend the city's people and interests, noted political scientist Peter Cheung.
Activist Wong Yeung Tat, founder of radical group Civic Passion, for instance, said his group did not take part in organising the protest but he had gone to Mongkok "to defend the people" after seeing the police officer fire the warning shots.
Indicating the depth of such suspicion of the establishment, a conspiracy theory that the riot was, in fact, staged by Beijing - so as to justify the implementation of the controversial anti-subversion law Article 23 - has been gaining strength.
"It sounds a little far-fetched. But the question is, why are so many people believing it? It boils down to the lack of trust in the Leung Chun Ying administration," said Dr Lee.
Beijing has slammed the protesters as "radical separatists" who are "inclined towards terrorism". There are noises about the need for Article 23.
Asked to what extent it believes its rhetoric, Prof Lau said the central government is very worried "localists" will be made use of by foreign forces.
For now, the city is divided over whether an independent inquiry should be set up to look into what happened. The Hong Kong government does not think so and has endorsed a police-led commission to look into operational aspects.
Prof Lau admitted this will "create cynicism" but argued that any investigative inquiry will not be able to produce a consensus in view of the divisions in Hong Kong.
But some say this is effectively "ostrich behaviour".
The government needs to heal the social divisions, move beyond the political reform impasse, improve its own governance performance and properly mediate other tensions between Hong Kong and the mainland, said Dr Cheung.
Otherwise, he added, "isolated incidents could trigger similar protests and conflicts in future".