Thai authorities have launched an investigation into how a Hong Kong bookseller, missing from a publishing company which had criticised Chinese state officials, managed to return to China despite no record of his leaving Thailand.

Gui Minhai was one of five publishers who went missing in disappearances which led to street protests in Hong Kong. Gui, Lui Bo, Cheung Ji-ping, Lee Bo and Lam Wing-Kei were all working for Mighty Current and Causeway Bay Books which were known for publishing dissident literature about high-ranking Chinese communist party members. Gui is thought to have headed to Pattaya, in Thailand, before he suddenly appeared on Chinese state TV on Sunday (17 January) to confess to a hit-and-run incident in 2004 which left a 20-year-old student dead.

His guilt, he said, had prompted his return but some believe the video was a fake citing a change in Gui's hairstyle and clothes changes between cuts, suggesting that the video has been put together from separate takes. It has also been claimed that he was reading from a script.

The 51-year-old was a nationalised Swedish citizen who was born in China and Swedish authorities had contacted both Thai and Chinese governments over the incident. Stockholm even summoned the Chinese ambassador over the case but the embassy in Beijing have not commented.

Thailand's Ministry of Foreign told the South China Morning Post that Thai authorities were "still looking into the case" but Bei Ling, a dissident poet and long-time friend of Gui's, said: "There was no record of him leaving Thailand," repeating a message reportedly from Swedish authorities that was passed to Gui's daughter, Angela.

On China Central Television (CCTV), Gui said he had decided to escape from China after receiving a suspended two-year jail term in 2004 in Ningbo, Zhejiang province. He said that he had killed a girl in a drink-driving accident.

After his disappearance, his friends began their own investigation, and Bei added that they reported that he could have gone to Pattaya after a reported sighting of him.

"Thailand is run by a military junta. The government may not think there are any problems with (Gui's) disappearance," he declared.