Although Hong Kong's mini-constitution guarantees the right to peaceful assembly, it was noted that, "restrictions are imposed, including those for preserving public safety and public order, and protecting the rights of others".
The group of activists were convicted for their involvement in a protest held on August 18, 2019, when organisers said 1.7 million people marched in protest of a proposed bill that would have allowed criminal suspects to be extradited to mainland China for trial.
The case is part of a push to disband Hong Kong's democratic institutions and clamp down on the opposition's moderate wing, according to professor of law and worldwide affairs Michael Davis, who is from the O.P. Jindal Global University in India and a former law professor at the University of Hong Kong.
The Hong Kong District Court found seven of them guilty of organizing and participating in an illegal rally.More news: GOP delegation demands answers amid escalating Biden border crisis
Prosecutors accused the group of defying police instructions that day and encouraging crowds to march across Hong Kong's main island, bringing traffic disruption.
Numerous seven have been at the heart of the pro-democracy struggle for years dating back to the Umbrella Movement in 2014 and even further.
The verdict is the latest in a series of historic setbacks in recent weeks for Hong Kong's pro-democracy camp.
The US said on Wednesday that Hong Kong does not warrant preferential treatment under the Hong Kong Policy Act, a law that had allowed Washington to maintain a special relationship with the city. While there was no violence and minimal disorder, prosecutors argued that the march violated Hong Kong's public order ordinance. The demonstration's organizer said 1.7 million people took place in the protest, which later saw violent clashes erupt with police.
After waves of pro-democracy protests, Beijing is increasingly cracking down on the city's rights and freedoms.More news: Biden sets out 'once-in-a-generation' $2 tn infrastructure plan
British lawyer David Perry, chosen by the Hong Kong government to lead the prosecution against the nine, ended up resigning to do so due to strong criticism from London and British legal organizations when it was learned that he had accepted it.
China introduced a controversial security bill to Hong Kong previous year after continuous mass protests.
Previously, two other defendants - former pro-democracy lawmakers Au Nok-hin and Leung Yiu-chung - had pleaded guilty to organising and taking part in an unauthorised assembly.
They will next appear in court on April 16, where mitigation pleas will be heard before sentences are handed down.More news: Suspect in Colorado shooting bought gun legally
Lee Cheuk-yan is facing three other trials this year on separate but similar charges, for organising unauthorised assemblies including a 2020 vigil for the Tiananmen Square massacre. Lai is the founder of media company Next Digital and a prominent supporter of the pro-democracy movement in Hong Kong. They have been charged under the national security law for taking part in an unauthorised anti-government protest in 2019.