Arrest by Chinese authorities of Hong Kong protestors attempted fleeing to Taiwan
Hong Kong 12, or 12 Hongkongers, are the twelve Hong Kong protesters, previously arrested by the Hong Kong police, detained by the Chinese authorities in 2020 on sea after a failed attempt to flee to Taiwan.
In a post on Chinese social media dated August 26, 2020, the China Coast Guard claimed that Guangdong authorities had intercepted a speedboat on August 23 under the suspicion of illegal border crossing, and that more than ten people had been detained. The released coordinates put the incident in the South China Sea, approximately from Hong Kong Island. On August 27, "The Guardian" cited two Hong Kong news outlets which reported, based on unnamed sources, that in the incident, a total of 12 people had been detained en route to Taiwan, of whom at least ten were Hong Kong residents. Referring to the same sources, the passengers had included activist Andy Li, who had been arrested on August 10 under charges related to the national security law and released on bail. Hong Kong police chief Chris Tang told media on August 27 that he had heard the reports on the detention, and that the force was actively seeking information from the mainland authorities.
Chinese authorities only released scant information on the situation of the detainees. 
On September 13, Chinese authorities announced that the detained had been brought to the Yantian Detention Centre in Shenzhen and put under "compulsory criminal detention". In a Twitter message from the same day, mainland government spokesperson Hua Chunying referred to the detainees as "elements" who had intended to separate Hong Kong from mainland China. Authorities repeatedly denied the detainees access to their families' appointed lawyers. Detention authorities claimed that the detainees had accepted government-appointed lawyers, which was denied by the families. 
Secretary of Security John Lee implied in statements made around that time that the Hong Kong government would not interfere with mainland law enforcement in the case.
On December 16, Yantian District authorities announced that a trial hearing was to be held in which the two oldest detainees, Quinn Moon and Tang Kai-yin, would be prosecuted for organising others to cross the border illegally, and eight prosecuted for crossing the border illegally. A trial hearing for the two underage defendants would be closed off to the public; they were returned to Hong Kong police on December 28, where they were facing extra charges for allegedly absconding.
At a December 28 trial – where no relatives, Hong Kong media, or foreign ambassador representatives were allowed to audit the hearing, contrary to what the court said –, eight of the ten defendants of age were sentenced to seven months of prison terms for illegal border crossing. Quinn Moon and Tang Kai-yin were sentenced to terms of two and three years, respectively. The eight defendants of age were returned to Hong Kong police on March22, 2021. They were held in quarantine upon arrival while local courts began hearings on their cases, with Andy Li being charged under the national security law.
The incident gained attention in Hong Kong and internationally, with US Secretary of State Mike Pompeo releasing a press statement on September 11 in which he expressed his concern both about the detainees' welfare as well as their lack of access to family-appointed lawyers. On December 29, 2020, the European Union demanded fair trials and the release of the 12 detainees.
Presumed identities of the detainees.
In its initial notice, the Guangdong Coast Guard released only the surnames of two of the detainees, Li and Tang, but no other information about names. The "South China Morning Post" reported that activist Andy Li was the Li referred to. As the full names were first published by pro-Beijing media Wen Wei Po, even some family members had doubts about their veracity. Meanwhile, the Hong Kong Security Bureau said that it had received advice from its mainland counterpart that the ages of the detainees ranged from 16 to 33. As of October 3, no one from Hong Kong has confirmed their identities. Two of the detained have British National Overseas passports, while a third has Hong Kong and Portuguese permanent residencies.
Background.
Although the capture happened on August 23, no information was released to the public by the Chinese coastguards until August 26. The social media post on August 26 only mentioned the GPS location, the time of arrest, and the number of Hong Kong residents detained.
On August 28, details about the presumed detainees were released to the public by "Wen Wei Po", citing "unnamed sources". According to "Radio Free Asia", the arrestees were presumably charged of "unlawful border crossing (into China territories)" and are currently in custody in mainland China. The media-published (not officially published by authorities) arrestee names include several Hong Kong pro-democracy activists, some of whom were earlier charged with protest-related crimes by the Hong Kong Police, and one under the new national security law.
According to state-affiliated newspapers, the 12 individuals set out at around 7am on August 23 from a dock located in eastern Hong Kong's Sai Kung. It is reported that they originally planned to reach Taiwan-controlled Pratas, also known as Dongsha Island, then change ship to reach Pingtung County. They were stopped and captured at around 9am at alleged GPS location (21°54'00"N, 114°53'00"E ), a location, if factually stated by Chinese authorities, that is not owned by China, but within its contiguous zone.
Responses.
Hong Kong and China Government responses.
August 27–28, 2020.
Hong Kong Police denied any cooperation with Chinese authorities in the arrest.
The Hong Kong Security Bureau confirmed having received information relating to the detainees from the Chinese government. The bureau promised to assist family members and detainees.
In Guangdong, the province of China where the coastguards were based, the public safety division and a spokesman of the provincial authorities declined to provide more details.
September 1.
Chief Executive Carrie Lam said in a press conference that the Hong Kong government would do its part to protect Hong Kong citizens, but if illegal activities occurred in another judiciary region, Hong Kong could not intervene.
September 4.
The human rights lawyers Lu Siwei and Ren Quanniu, who had been appointed by the detainee's family members, were denied meeting access. Both of them reported that Chinese officials had attempted to dissuade them from pursuing the case.
September 13.
After the detainees' family press conference from the day before, in which they had pleaded for intervention by the Hong Kong government and possible extradition, Yantian detention center officially confirmed, for the first time, that the 12 detainees were indeed located in Yantian. Meanwhile, Chinese foreign ministry spokeswoman Hua Chunying publicly stated on Twitter that the 12 detainees were criminals trying to "separate Hong Kong from China", a more serious allegation than the "illegal border crossing", and a crime punishable under the Hong Kong national security law. The Hong Kong government reaffirmed its stance not to interfere with China's jurisdiction, claiming that the relevant crime "falls within the jurisdiction of the mainland and the special administrative region government respects and will not interfere with law enforcement actions."
September 19.
Secretary of Security John Lee acknowledged in a TVB interview that Hong Kong authorities had only been informed of the capture five days after, and claimed that all 12 detainees were in good health. He further claimed that the detainees had already chosen their lawyers provided by China. Separately on a radio interview, Chief Secretary Matthew Cheung said that "Hong Kong’s Immigration Department, and the Hong Kong Economic and Trade Office in Guangdong had communicated with the families 80 times since the arrests" but claimed that their hands were tied.
September 26.
The Hong Kong government issued a press release informing the public that the 12 detainees were now approved to be "arrested". Hong Kong Police also released a report with some data such as speed and coordinates of the boat to clarify the public's concern. According to criminal law in China, the maximum number of days of detention before sending them to the normal criminal court process – a certain form of incommunicado detention – or release on bail is 37 days.
September 30.
At the end of the 37-day legal limit for detention without further action, two of the 12 were formally charged with organizing smuggling and the remaining 10 individuals were charged with "illegal border crossing".
October 10.
Hong Kong police arrested a group of nine people who allegedly had provided financial and other assistance to the detainees before their voyage, and for after their arrival in Taiwan.
October 12.
Hong Kong Chief Executive Carrie Lam made clear that she "no longer wish[es] to discuss matters related to these 12 individuals" when asked by a journalist in a press conference on that day about her effort to safeguard the 12 individuals as she was to visit Shenzhen.
October 23.
A request in the Legislative Council to put the 12 detainees on the next meeting agenda, and to have Security Secretary John Lee report on the situation of the detainees as well as the support given to them and their families, was voted down by the pro-Beijing majority.
October 28.
Activists familiar with the matter told reporters in a group chat that at least five family-appointed lawyers had received verbal warnings from various levels of Chinese justice bureaus to drop the work for their clients. Prior to this, on October 22, five family-appointed lawyers had visited the detention centre but were again refused entry on the grounds that the detainees had already been assigned two lawyers; family-appointed lawyer Lu Siwei suspected that these might be government-appointed.
November 20.
It was reported that seven out of the 12 detainees had written letters to their families, with the earliest dated October 13. There were suspicions that the handwritten letters, which stressed that the detainees were treated well, had been dictated by authorities.
November 27.
Police in the Yantian district of Shenzhen said in a posting on Weibo that they had completed their investigation into the case of the 12 detainees, and that they would be sent to the Yantian District People's Procuratorate for "examination and prosecution". There has not been a visit granted since the capture.
December 16.
The Chinese government released the names of the now-confirmed detainees' names along with the charges the government was pressing. It said that the two underage detainees' trials would not be open to the public.
December 25.
Chinese government officials advised the family members that trials would begin three days later, on December 28.
December 28.
At the trial of 10 of the 12 detainees, staff maintained that it was open to the public, but immediately followed this with the advice that the gallery was full. On these grounds, representatives from the United States (which had applied for an audit in accordance with established procedures), the United Kingdom, Canada, France, Germany, Portugal, Australia and the Netherlands were denied access to the hearing. Eight of the ten defendants of age were sentenced to seven months of prison terms for illegal border crossing. The two oldest detainees, Quinn Moon and Tang Kai-yin were sentenced to terms of two and three years, respectively.
December 30.
Two defendants aged 17 and 18 years were returned to Hong Kong by mainland authorities. The Yantian People's district court said that they had admitted wrongdoing, and that it would not persecute them.
Aftermath.
The eight activists of age were returned to Hong Kong police on March22 and charged by local courts. It was announced on March24 that security law charges had been laid against Andy Li. The "Apple Daily" reported on March28 that according to its sources, Li had been transferred to solitary confinement at a psychiatric hospital. On March30, a lawyer representing Li appeared in West Kowloon Magistrates' Courts, with Li absent as he was still in quarantine isolation. An associate of the lawyer confirmed that they had met Li, but did not disclose information on Li's whereabouts. The family asserted that they had no knowledge of the lawyer.
On April 5, 2021, after completing a two-week quarantine period in relation to the COVID-19 pandemic, five of the activists who had been handed back by mainland authorities appeared in a court in Sha Tin over local charges in relation to the 2019–2020 Hong Kong protests. They did not apply for bail and were to appear again in court the following month.
On September 2, 2021, eight of the activists, including the two who had been transferred to Hong Kong on December, appeared in court on charges of trying