Image copyright PA Image caption Hannah Witheridge and David Miller were found dead last year

DNA from a garden hoe allegedly used to kill two British tourists on a Thai island does not match samples taken from two men accused of the killings, a court in the country has heard.

Forensic expert Dr Pornthip Rojanasunand also criticised a failure to analyse blood found at the scene.

David Miller, 24, from Jersey, and Hannah Witheridge, 23, from Great Yarmouth, Norfolk, were found dead on a beach on Koh Tao last September.

Zaw Lin and Wai Phyo deny the killings.

Police say DNA on the victims' bodies matches that of the accused.

But officers have already testified that they failed to take DNA samples from the alleged murder weapon, examining fingerprints instead.

Dr Rojanasunand, who heads a forensic unit run by the Ministry of Justice, said she had subsequently extracted two samples of DNA from the alleged weapon.

Both were from males, but neither matched the defendants, she told the court. Anyone holding the hoe for more than 15 seconds would have left DNA, she added.

Dr Rojanasunand also questioned a decision to move Miss Witheridge's body from where she was killed - potentially destroying other evidence.

Image copyright Reuters Image caption Zaw Lin and Wai Phyo deny killing the British pair

The trial previously heard evidence from a police officer, who described severe injuries Miss Witheridge suffered and evidence she had been raped. Mr Miller's body was discovered with severe head injuries several metres away, he said.

The prosecution says a DNA match between samples found on Miss Witheridge's body and the two defendants is central to its case.

Defence lawyers had asked for the samples to be independently verified but were told there was nothing left of them to re-test.

Police, however, agreed to hand over the garden hoe which was the alleged murder weapon, along with a shoe and a plastic bag.

BBC South East Asia correspondent Jonathan Head said a verdict is not expected until October.