This year, Thai police relaunched the hunt for the killer of Kirsty Jones, the daughter of a Welsh farmer, who was raped and strangled in a Chiang Mai guesthouse, after the original investigation was declared incompetent.

But eight months after saying that witnesses would be re-interviewed, authorities have yet to release the paperwork which would allow British officers to question witnesses in the UK.

Jones, 24, from Brecon, Powys, had just graduated from Liverpool University and was on a world tour when she was murdered on August 10, 2000, at the Aree guesthouse in Chiang Mai.

A string of suspects were charged or arrested, and subsequently cleared and released.

Dyfed-Powys Police, who helped the Thai authorities to secure the killer's DNA, say they now have the "key" to the crime and it is vital that they be allowed to speak with witnesses to get the killer's name. According to the genetic profile, the killer is a Thai man. Any of the British witnesses who were in Thailand at the time of Jones' death might hold clues to his identity.

Chief Inspector Steve Hughson, of Dyfed-Powys Police, said: "There are witnesses back in the UK and we feel, and the Thais feel, there might be some merit in speaking to them now. In order to do that, on the Thais' behalf, we need a letter of request, an official document."

Royal Thai Police are understood to have written to the Thai attorney-general months ago asking that British police be allowed to question "two or three" witnesses, but permission has yet to be granted.