DNA evidence collected from the weapon allegedly used to kill two British backpackers in Thailand does not match samples from the two men currently standing trial for their murder, a forensic expert has claimed in court.

Britons Hannah Witheridge, 23, and David Miller, 24, were brutally killed on Sairee beach last year in September. The case shocked the world, drawing international attention.

Forensic expert Dr Pornthip Rojanasunand told Koh Samui’s court although her team had found two men’s DNA on the alleged murder weapon, a garden hoe, it did not match that of Burmese workers Zaw Lin and Wai Phyo, currently standing trial for murder.

Hannah Witheridge and David Miller, who were murdered on a beach in Thailand in September 2014 (PA)

She also criticised police officers’ failure to analyse blood found at the crime scene.

It is the latest inconsistency in a case criticised for its bungled handling.

During a three-month trial, officers have been accused of intimidation, abuse of witnesses and improperly collecting evidence from the scene. They already testified they had failed to take DNA samples from the alleged murder weapon, instead relying on fingerprints.

They deny any wrong-doing.

The prosecution has argued that DNA evidence is central to its case, but the Thai court turned down requests from defence lawyers for the evidence to be independently tested.

In pictures: Thailand beach murders Show all 12 1 /12 In pictures: Thailand beach murders In pictures: Thailand beach murders Thailand beach murders Two Myanmar migrant workers Win (left) and Saw (right) are suspects in the killing of two British tourists EPA In pictures: Thailand beach murders Thailand beach murders Two Myanmar migrant workers suspected of killing two British tourists participate in a crime re-enactment EPA In pictures: Thailand beach murders Thailand beach murders The two suspects (wearing hard hats) during a re-enactment of the alleged crime Reuters In pictures: Thailand beach murders Thailand beach murders Thai policemen conduct DNA tests on staff from two beachside bars as part of the investigation on the murder of two British tourists on the southern resort island of Koh Tao In pictures: Thailand beach murders Thailand beach murders Police chiefs look at a beach near the spot where bodies of two killed British tourists were found on the island of Koh Tao Getty Images In pictures: Thailand beach murders Thailand beach murders Police in Koh Tao said they were liaising with officers in Bangkok to try and detain the second man EPA In pictures: Thailand beach murders Thailand beach murders People of Koh Tao offer their prayers In pictures: Thailand beach murders Thailand beach murders A Thai villager lays flowers during a memorial service for two murdered British tourists at the crime scene on a beach of Koh Tao resort island EPA In pictures: Thailand beach murders Thailand beach murders A police searches for clues near the spot where bodies of two killed British tourists were found, on the island of Koh Tao In pictures: Thailand beach murders Thailand beach murders Thai workers carry the bodies of two British tourists on Koh Tao island in the Surat Thani province of southern Thailand Getty Images In pictures: Thailand beach murders Thailand beach murders Hannah Witheridge, 23 was killed on the small island of Koh Tao on 15 Septembe In pictures: Thailand beach murders Thailand beach murders David Miller, 24, was killed on the small island of Koh Tao on 15 September

But Dr Rojanasunand, who heads the country’s Forensic Institute, was able to obtain items recovered from the scene – including the garden hoe, a shoe and a plastic bag – for the lawyers of the two Burmese men.

The forensics expert also queried officers’ decision to move Ms Witheridge’s body from where she was killed – potentially removing vital evidence.

A Thai villager lays flowers during a memorial service for two murdered British tourists at the crime scene on a beach of Koh Tao resort island (EPA)

The Jersey backpacker’s body was found several metres from Mr Miller. Both victims suffered severe head wounds and officers alleged in court there was evidence Ms Witheridge had been raped.