Hongkongers being held by authorities over the border on suspicion of breaching mainland law is not unheard of. But the recent capture at sea of 12 locals escaping criminal charges in relation to the newly enacted national security law and the social unrest last year has understandably aroused wider concerns. While circumstances have made the case more sensitive, the legitimate rights of the accused still remain. Little is known since the mainland authorities confirmed the arrests on suspicion of unlawfully crossing the border. The activists are currently detained in Shenzhen after their vessel was intercepted by the mainland coastguard outside Hong Kong waters last month en route to Taiwan. Among them are a 29-year-old arrested under the national security law in July, and criminal suspects involved in the extradition bill protests. The differences in the two legal systems have always been a concern to those running into trouble on the mainland. Coming after the unrest fuelled by the now-withdrawn extradition bill, under which fugitives could be tried across the border, the case has attracted even more attention. The circumstances of the arrests and the trials facing the suspects on the Hong Kong side have inevitably added to the sensitivity. This is not helped by the lack of transparency on both sides of the border. There were reports of lawyers being repeatedly denied access to the detainees and facing pressure and criticism for representing them. Such reports do not square with the institutional arrangements provided for criminal suspects under the mainland legal system. Notwithstanding the absence of an extradition treaty, fugitives have been returned to the city to face criminal proceedings before. Police are understood to be seeking the return of all the suspects. Chief Executive Carrie Lam Cheng Yuet-ngor said it was not a question of simply having them returned to the city, because mainland legal procedures had yet to be completed. However, that should not compromise the legitimate legal rights of the accused. The cases should be handled in accordance with mainland law and practices involving those from Hong Kong.