Chinese officials told authorities in Hong Kong late Monday that Lee Bo, the chief editor of a Hong Kong book publishing company banned in China, was on the mainland. Five booksellers linked to Mighty Current and its Causeway Bay bookshop have gone missing since last year, triggering speculation that China is extending its controls on free speech to Hong Kong.

Police officials in Hong Kong confirmed late Monday that they received a note from Guangdong province's public security department saying Lee was "understood" to be on the mainland, the Associated Press (AP) reported. Hong Kong police also said that Chinese officials forwarded a letter to them from Lee, which was similar to one he wrote his wife earlier, saying he “voluntarily” went to the mainland to help authorities in an investigation. The handwriting seen in the latest letter was confirmed by his wife to be Lee's.

According to a report by the South China Morning Post (SCMP), Lee reiterated in the latest letter that he was helping Chinese authorities in investigations. Lee also reportedly blamed his associate Gui Minhai, a Swedish citizen who has been missing for three months now, for getting him involved in the investigation. The whereabouts of the other three booksellers are still unknown. 

Lee’s disappearance triggered widespread concerns in Hong Kong owing to suspicions that Chinese security agents abducted him from Hong Kong. Lee, who had raised an alarm in October after four of his associates went missing, was last seen at the company’s warehouse and did not have a permit with him to travel to the mainland. However, he reportedly called his wife from Shenzhen days after he went missing, AP reported.

Gui was seen on national television Sunday night where he admitted that he had turned himself over to Chinese authorities over his involvement in a fatal car accident in China 12 years ago. Hours after the broadcast, Gui’s daughter Angela reportedly received a message from her father’s Skype account, saying: “Hi Angela, I’m ok. Please don’t worry about me. I have returned to China on my own to sort some personal problems. If anybody asks about me, please keep quiet.”

Before his disappearance, Gui was working on a book about Chinese President Xi Jinping’s “love affairs,” according to reports.

While human rights activists reportedly suspect that Gui was forced to make a confession, Angela described the confession as “ridiculous” and contrived, according to SCMP. Swedish authorities have been demanding “openness” from Beijing over the case, and it's been speculated that Chinese agents kidnapped him while he was on a holiday in Pattaya, Thailand.

“We encourage the Chinese authorities to show us much openness, and provide information and contact between the Swedish authorities and the detainee,” Per Bolund, Sweden’s deputy minister for finance, told SCMP, adding that he hoped Chinese authorities would allow Swedish officials to “meet Gui Minhai himself.”

Bolund also said: “I really hope that the Chinese authorities would see this need and that it would be the easiest way to resolve all these questions that have arisen,” according to SCMP.