HONG KONG, July 6 (Reuters) - One of the Hong Kong democracy activists who was returned from a Chinese jail after being captured at sea last year, pleaded guilty in court on Tuesday to charges of attempted arson and possessing dangerous objects. Hoang Lam Phuc, 17, was among a group of 12 people intercepted by mainland authorities in August 2020 on a boat believed to be en route to Taiwan, in a case which drew international attention and concern over their treatment in China. Hoang pleaded guilty in the District Court on the charges, which were related to Hong Kong"s pro-democracy protests in 2019. In the afternoon, he appeared in the same court with eight others who were captured by China in a separate case in which they are accused of "intending to pervert the course of public justice," namely obstructing police investigations by fleeing the Hong Kong jurisdiction. Hoang"s lawyer said he intended to plead guilty but did not make a formal plea. The rest asked for more time to seek further legal assistance and were told by Judge Justin Ko to return to court on September 2. Hoang will return on July 26 for both his cases. At the time of their capture, all 12 were facing charges in Hong Kong over the 2019 protests. In China, they were sentenced to between seven months and three years for illegally crossing the border, or organising the crossing. Two minors were released in December, while eight others were released in March. Tang Kai-yin and Quinn Moon, sentenced to three and two years, respectively, are still in a Chinese prison. Andy Li, who faces separate charges of "conspiracy to commit collusion" with a foreign country under Hong Kong"s new national security law was not among those who were in court on Tuesday. read more All returned activists were detained in Hong Kong as soon as they arrived from the mainland. During the detention of the 12 in the southern Chinese city of Shenzhen, mainland authorities denied their families and lawyers access, insisting they be represented by officially appointed lawyers, provoking criticism from rights groups. Diplomats and journalists were not allowed to attend their trial in China. Chinese authorities had said their case was handled "in accordance with the law."