Chinese authorities have confirmed that they are holding all five men linked to a Hong Kong publishing house who went missing in recent weeks.

The Hong Kong Police Force said in a statement Thursday that it had had received a response from the public security department in China’s Guangdong province that said Lui Por, Cheung Chi Ping and Lam Wing Kee were under investigation, and that “criminal compulsory measures were imposed on them.” The three were previously unaccounted for having gone missing during visits to mainland China.

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The three men “were suspected to be involved in a case relating to a person surnamed Gui, and were involved in illegal activities on the Mainland,” the Hong Kong police statement said, referring to Gui Minhai, one of the two other booksellers already known to be held in China.

All five men are connected to publishing company Might Current Media, which produces books containing salacious allegations about the private lives of Communist Party leaders. Co-owner Gui went missing while staying at his home in Thailand, only to turn up last month on Chinese state TV giving an apparently scripted confession to an 11-year-old drunk driving incident. Gui’s partner, Lee Bo, has confirmed that he is “assisting” an investigation in mainland China, where he has been visited by his wife. Lee went missing while in Hong Kong, sparking fears that the Chinese government was undermining the territory’s semiautonomous status.

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Chinese state security also passed their Hong Kong counterparts a letter from Lee declining a request to meet with him. “He [Lee] would contact Police should he need to meet with Police,” the statement said, adding that the handwriting in the letter had been authenticated by Lee’s wife.

Hong Kong police also said they had asked the Chinese authorities for more information on Lui Por, Cheung Chi Ping and Lam Wing Kee’s situation, “and to pass on a message to Lee [Bo] that Police still wanted to meet with him as soon as possible.”

Amnesty International called for the Chinese government to explain what charges the men face and disclose where they are being held.

“The latest official disclosures about the last three missing book publishers are anything but satisfactory,” William Nee, China researcher for Amnesty International, said in a statement. “The Chinese authorities need to end their smoke and mirrors strategy and come clean with a full and proper explanation.”

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Write to Simon Lewis at simon_daniel.lewis@timeasia.com.