Two Thai fishermen have appealed against their death sentences for the rape and murder of Cardiff student Katherine Horton on New Year's Day.
The men's lawyer said they did not know what their sentence would be
Wichai Somkhaoyai, 24, and Bualoi Posit, 23, were handed the death penalty for the killing on Koh Samui.
The pair's lawyer claimed they were convicted solely on DNA evidence and that they confessed to her murder "out of a sense of remorse".
Human rights groups have voiced concern at the speed of the men's trial.
The men received the sentence of death by lethal injection a week ago at a court in the southern Thai province of Surat Thani. The sentencing judge said their crime had "terrified people".
Both had pleaded guilty to raping and killing 21-year-old year old Miss Horton, who was on holiday with a fellow student from Reading University.
Thai authorities moved swiftly in the criminal investigation after Thai Prime Minister Thaksin Shinawatra intervened, saying the student's killers should be executed because they had harmed the country's reputation.
On Wednesday, the fishermen's lawyer said they were appealing on grounds that the death penalty was "too harsh" and that their conviction was secured without eyewitnesses.
Amarin Nuimai said that his clients had co-operated with police and confessed to Miss Horton's murder without knowing the consequences.
Katherine Horton's body was found on 2 January
"Both of them had little education. They didn't even know what the maximum sentence they could face, so we have asked the court of appeals to reconsider the death sentences," Mr Nuimai told AFP news agency.
A 29-page document outlining the appeal has been submitted to the authorities.
The lawyer said he expected the appeals court to consider the high-profile case, given that it was a gruesome crime that affected Thailand's reputation.
Miss Horton was attacked as she made a mobile phone call on Koh Samui's Lamai beach, where she and her friend had rented accommodation during their New Year break.
The fishermen's trial heard she was beaten with a parasol pole, raped and later dumped out at sea, where she drowned.
The murder happened on the beach where the student was staying
The fishermen, the judges were told, had been watching pornographic films on their boat before swimming ashore to make the attack.
After the trial, Miss Horton's family thanked Thai police for "their diligent and speedy apprehension of the offenders".
But Fair Trials Abroad and Amnesty International criticised the speed of their sentences.
Amnesty International said it was concerned about the speed of a trial held amid political pressure for a quick resolution.
Fair Trials Abroad said it was not aware of a death sentence being imposed in similar murder cases in Thailand.