Laura Witheridge, sister British backpacker Hannah Witheridge, who was raped and murdered along with her partner David Miller on the island of Ko Tao in Thailand, has said she has received death threats from Thai individuals since her sister's murder.

Laura, in a social media post, said the Thai Police had provided no update to her family when they went to Thailand to receive her sister's body, and that they botched the investigation. She also alleged that sinister activities were going on in the island of Ko Tao, where numerous deaths have been reported as suicides and accidents.

"What if I told you that when we went to Thailand to bring Hannah home, we were offered the opportunity to go to the Royal Thai police headquarters for an 'official update'... but that, on arrival, we were taken into a large room, left for 5 minutes before the door opened and around 200 journalists were allowed into the room and we were ambushed by this mob of hungry journalists shoving cameras in our faces, (sic)" wrote Laura.

Her post warns travellers against visiting Thailand, calling it a lion or tiger, something that is aesthetically beautiful but essentially dangerous.

"What if I told you that since we lost Hannah there have been many more suspicious deaths on Ko Tao. You probably haven't heard of them all, as not all were British Nationals. The deaths, where possible, are covered up as suicides and accidents. This would have happened with Hannah, if it had not been for the hideous brutality of her passing, (sic)" said Laura on Facebook.

Hannah, 23, and David, 24, had been found murdered on the Sairee beach in Ko Tao in September 2014.

Burmese migrants Zaw Lin and Wai Phyo have been convicted for the deaths. The pair, who had initially confessed, later withdrew their statement saying they were tortured by the police to obtain their confession.

While the defence team alleged that the Thai Royal Police had mishandled important DNA evidence, David Miller's family, which was present at the sentencing of the migrants, told reporters justice had been served, reports The Guardian.

The Thai Royal Police have also said if Laura is receiving threats, they would be ready to help her with the investigation if she wished to pursue it.