Thai police have said the FBI is welcome to monitor their investigation into the death of Kill Bill star David Carradine in a luxury Bangkok Hotel last week.

“The FBI can observe or ask Thai investigators to investigate certain points but it cannot run its own investigation or collect evidence,” said senior attorney general Sirasak Tiypan.

Mr Sirasak said there was no reason to deny such a request by the FBI, adding that Thailand had granted permission for several such observations by US officials in the past.

Bangkok police are still awaiting the results of laboratory tests which will take up to four weeks before they can make an official conclusion about the cause of Carradine’s death.

An initial autopsy report revealed that the actor died from a sudden lack of oxygen and his body showed no signs of struggle.

Police Colonel Somprasong Yenthaum, who is leading the probe, said on Sunday he was, “confident we are working on the right track” and added that US embassy representatives had witnessed the examination of the hotel room.

Carradine was in the Thai capital to shoot a film called Stretch when he was found dead, naked and curled up inside the wardrobe with one end of a shoelace tied around his penis and the other end fastened around his neck, in the wardrobe of the Swissotel Nai Lert Park hotel by a housekeeper.

The director of Thailand’s Central Institute of Forensic Science (CIFS), Kunying Porntip, said he could have been be trying autoerotic asphyxiation to gain sexual pleasure and may have accidentally suffocated.

Carradines family have vigorously disputed claims he may have committed suicide and also rejected the kinky masturbation-sex angle.

David Carradines family have employed high-profile forensics expert Dr. Michael Baden to perform an autopsy on the dead actor in the US.