Legal and foreign affairs units from Thai police are examining whether Laura Witheridge, sister of murdered backpacker Hannah Witheridge, had broken any laws following a lengthy Facebook post detailing remarks made to the family during the investigation.

Eastern Daily Press: Thailand island of Koh TaoThailand island of Koh Tao (Image: Archant)

In a public post on Facebook, which appeared online on Monday but has since been removed, Laura Witheridge told how she was targeted with death threats and sent disturbing photos after the death of Hemsby student Hannah on a Thai island.

She alleged that the family were asked by court officials 'Why are you so bothered? Just go home and make another one.'

She also said they were offered compensation to 'keep quiet'. She added: 'Obviously we were absolutely appalled and told them to shove it.'

But Thai media reported that the national police chief, Chakthip Chaijinda, said they were looking into whether Miss Witheridge had broken any laws, as defamation is a criminal offence in Thailand.

Meanwhile, the Thai Court of Justice said it has held preliminary inquiry into the claims made by Miss Witheridge.

In a statement in the national press, a spokesman said there was 'deep concern' over allegations 'implicating that inappropriate remarks were made on the death of Miss Hannah Witheridge by judges and court officials at the trial.'

'The office of the judiciary has promptly conducted a preliminary investigation,' the spokesperson said.

'Throughout the trial, neither complaint nor any improper conduct was brought up for an immediate action to be taken ... Moreover, all judges and court officials are consciously aware of the rights of the victim and her family afforded by law,' it said, adding that the Witheridges were entitled to submit a formal complaint.

The Facebook post had been shared thousands of times, including by the hackivist collection Anonymous, who claimed responsibility for hacking 14 Thai police websites the week before.

The bodies of Hannah Witheridge, 23, and David Miller, 24, were discovered on a beach on the holiday island of Koh Tao on September 15, 2014.

Zaw Lin and Wai Phyo, also known as Win Zaw Htun, initially confessed to the killings but later retracted their statements - claiming they had been tortured by police.

Prosecutors said DNA evidence found on cigarette butts, linked the men, both from Myanmar, to the killings.

Their account was disputed by the defence team who said evidence was mishandled by police and that the case had been dogged by chaos and error from the start.

The guilty verdict and death penalty, also sparked angry protests in Myanmar. The defence is expected to lodge an appeal.