The trial of two Burmese men accused of killing a Norfolk student on a Thai beach could be close to collapse, according to reports.

Eastern Daily Press: Hannah Witheridge and David Miller.Hannah Witheridge and David Miller.

After three days of evidence last week, defence lawyers and a human rights activist representing Myanmar nationals Zaw Lin and Win Zaw Tu have called for the case against them to be dropped.

The pair are accused of killing Hannah Witheridge, of Hemsby, near Great Yarmouth, and David Miller, of Jersey, on the small island of Koh Tao last September.

Last week, the Witheridge family flew to the neighbouring island of Koh Samui for the opening days of the trial.

It is understand they are now back in the UK but, having raised the £15,000 needed to attend the case and pay for an interpreter through an online petition, they are likely to return to Thailand when the trial starts again on July 22.

In the meantime, confusion over whether DNA evidence can be re-tested continues.

On Friday, judges at the Koh Samui court gave the defence team permission to independently retest all the police's DNA samples - but police officers said the evidence had 'finished' and could not be reexamined.

Speaking to the AFP news agency Andy Hall, a Thailand-based British rights activist who has raised money for the accused and advises their legal team, said: 'The court order means no possible retest on DNA samples from Hannah and David's bodies.

'Zaw Lin and Wai Phyo (Win Zaw Tun) now have no chance to retest crucial Thailand based forensic evidence implicating them in the crimes they are charged of.'

He added that the integrity of the police investigation 'has been seriously undermined' by the lack of retestable samples.

The trial has drawn global attention. Initial reports said the DNA evidence had been lost but police said that was a misunderstanding.

They have reportedly told defence lawyers that at least in some cases, the samples were used up by the initial testing. But no clear official explanation has been issued.

'It is not lost,' national police chief General Somyot Poompanmoung told reporters in Bangkok. 'I repeat: Nothing is lost.'

Gen Somyot called it a misunderstanding that stemmed from foreign media covering the case who might have poor Thai language skills.

He said the local police investigator, Lieutenant Colonel Somsak Nurod, was vague in his evidence and therefore was misinterpreted.

Lt Col Somsak was no longer in possession of the DNA evidence since he collected it and then sent it to the Forensics Medicine Institute in Bangkok, Gen Somyot said.

'Nothing is missing. It's a misunderstanding,' he said.

Speaking before the trial started last Wednesday, Miss Witheridge's heartbroken family issued a statement in which they said they wanted a fair and just trial.

The family, who run self-catering holiday parks in Hemsby, Newport, Winterton and the Broads, said they were 'united in grief' with Mr Miller's loved ones.

They said: 'Hannah was a beautiful person, inside and out, she brought a room alive just being there.

'She was fun, honest and loved life. Her bright future was brutally ended leaving those who loved her broken with no answers.

'Speculation, rumour and theory have been incredibly hurtful to our family and Hannah's friends, making an already unthinkable time harder to bear. We of course want to see those responsible for the brutal murder of our precious girl brought to justice.'