National security police are holding a fourth activist from Student Politicism for conspiring to incite subversion.
Wong Yuen-lam, 19, gave herself up at Mong Kok police station shortly after midnight yesterday, two days after the arrest of three members of the group.
The group's spokeswoman, she was held for breaching articles 22 and 23 of the national security law and faced up to 10 years imprisonment. She is also the secretary of the Polytechnic University's student union.
Sources said Wong had been one of the targets for arrest but the security police failed to track her down since the Monday operation.
On Tuesday, the other three appeared in a West Kowloon magistrates' court jointly charged with conspiring to incite subversion.
They were group convener Wong Yat-chin, the group's convener, Chan Chi-sum, ex-secretary general, both 20, and ex-spokeswoman Chu Wai-ying, 18, a Baptist University student.
Principal magistrate Don So Man-lung rejected their bail applications and remanded them until November 3 for the case to be transferred to the district court.
Meanwhile, Cheung Sha Wan Community Establishment had ceased operations as of yesterday.
Group chairman and Sham Shui Po district councilor Lee Man-ho said the unpredictable political environment made it unsuitable for the group to continue operating.
Lee is to take an oath to uphold the Basic Law and pledge allegiance to the SAR and China tomorrow among the second batch of district councillors to be sworn in.
Last year, Lee made headlines after posting a notice that said "blue ribbon [pro-establishment supporters] and dogs [policemen)]cannot enter" outside the office he shares with ex-Sham Shui Po district councillor Andy Lao Ka-hang.