By Amy Sawitta Lefevre
BANGKOK (Reuters) - Thai Prime Minister Prayuth Chan-ocha defended a police investigation into the murder of two British tourists on Friday, amid criticism of shoddy forensic work and concern that two arrested Myanmar men may have admitted the crimes under duress.
Zaw Lin and Win Zaw Htun, both 21, were arrested last week for the murders of British backpackers Hannah Witheridge, 23, and David Miller, 24.
The bodies were found on a beach on the southern island of Koh Tao, or Turtle Island, famous for its coral reefs and diving. Post-mortem examinations by Thailand's forensics department showed that Miller died from drowning and blows to the head while Witheridge died from severe head wounds.
The killings have dealt a blow to Thailand's vital tourism industry, which accounts for 10 percent of gross domestic product. The country is under martial law after a May coup and its tourism sector is struggling to recover after months of political protests that kept many away from the capital Bangkok.
"I would like the media to stop speculation and let investigators do their work," Prayuth told reporters after landing back in Bangkok following a two-day visit to Myanmar.
"We must build foreign confidence and make Britain and other foreign nations understand. They might be a little surprised why the criminals were caught so quickly. I myself was excited."
Prayuth added that authorities would not "dare catch the wrong person".
"I want all Thais to stop and think that authorities have procedures in place. Nobody would dare catch the wrong person because this is a case of big international interest."
Police said the arrested men had confessed to the crime, despite the fact that the two had yet to appear in court to face any charge and speak for themselves.
Around 10 protesters gathered in front of City Hall in Myanmar's capital Yangon on Friday during Prayuth's visit to the city calling for a fair trial.
"Instead of investigating systematically, Thai police charged Myanmar workers with murder and announced it quickly to the international media," said rights activist Nay Myo Zin.
"I would like to urge our government to put pressure (on Thailand) and get help from the international community so that the real story can be found out."
The murder inquiry has been dogged from the outset by contradictory statements by officials. Police were widely accused of bungling the investigation, including chasing the wrong leads and failing to seal off the crime scene quickly enough, and pressure grew for them to solve the crime quickly.
Aung Myo Thant, a lawyer contracted to defend the suspects, has called the case a "set-up".
He was not available for comment.
On Thursday Khunying Porntip Rojanasunan, director-general of the Central Institute of Forensic Science, questioned methodology used in the case.
"The weak point (in the investigation) is that police do not understand that the case requires a forensic pathologist," she was quoted as saying by the Bangkok Post English-language paper.
Police have strongly denied allegations of abuse during the investigation and have stressed the importance of DNA evidence in the case. DNA found on Witheridge matched samples taken from the two men, police said.
Thai national police chief General Somyot Poompanmuang has called the investigation "a perfect job".
(Additional reporting by Win Myint in YANGON; Editing by Nick Macfie)