"Missing" Hong Kong bookseller Lee Bo reunited with his wife in the Chinese mainland on Saturday, insisting that he voluntarily traveled to the mainland and cooperated with investigators, asking Hong Kong police to stop their investigation, Hong Kong-based Sing Tao Daily reported on Sunday.

Hong Kong police confirmed on Sunday that Lee's wife sent them a letter written by Lee, and issued on the same day another request for assistance from Guangdong police in arranging a meeting with Lee.

Hong Kong police previously requested to meet him after receiving a letter on his whereabouts from Guangdong police on January 18.

According to a statement on the official website of Hong Kong police, it said that police was informed by Lee's wife that she had met with Lee on Saturday afternoon at a guesthouse in the mainland. She said in the statement that Lee was in good health and his spirits were fine, and said that he was assisting in an investigation as a witness. After the meeting, Lee asked her to pass on a letter addressed to the Hong Kong police.

According to the Sing Tao Daily, Lee said in the letter that he appreciated the police's concern and clarified that he had neither been kidnapped nor arrested for prostitution in the Chinese mainland.

"I have already met with my wife and I am free and safe here. My wife told me that, after she received my phone call, she was not going to call the police. But later she changed her mind after some people spoke to her. She closed the case after realizing she was being used," read the letter.

Lee also said that he hopes the Hong Kong police would not waste police resources on him and stop their investigation. "I came to the mainland to voluntarily cooperate with investigators, and it took some time to solve my personal and company affairs. I hope society respects my privacy and gives some space for me and my family. I earnestly request police protection for my family from harassment," said the letter. 

Police said that the letter was similar to previous ones Lee wrote. Lee's wife did not provide details of their reunion or the nature of the investigation Lee underwent.

Lee, who co-owns a bookstore in Causeway Bay, was reported missing on December 30. His disappearance, with another four booksellers, triggered protests in Hong Kong and sparked speculation that they were secretly taken away for questioning for publishing books against China.