But five days after David Miller, 24, and Hannah Witheridge, 23, were bludgeoned to death on scenic Koh Tao in the Gulf of Thailand, police appear to have no clues as to the identities of the killers.
Suspect Christopher Ware, 25, who was a travelling companion and room-mate of Mr Miller, has been cleared and allowed to fly to London.
Mr Ware became a suspect when police found trousers with what was thought to be blood in Mr Miller's luggage. Tests showed the stain to be dirt.
Contrary to media reports the island has never been locked down since the killings early Monday, with ferries and boats freely coming and going as usual.
Despite the fact that tourists were allowed to enter the crime scene at a rocky cove in the hours after the bodies were found, forensic tests have revealed that DNA from semen recovered from Ms Witheridge's body matched DNA on a cigarette butt found at the crime scene.
But the DNA did not match samples taken from Mr Miller, Mr Ware or migrant workers from Burma (Myanmar), who were among those initially detained and interrogated by police.
Ms Witheridge and Mr Miller met each other while staying at the same bungalows on the island and were seen together on the night of the attack.
Surat Thani police Major-General Kiatpong Khoasam-ang told reporters that one scenario is that two men had shared a cigarette about the time Mr Miller and Ms Witheridge had walked past them heading to the rocky cove where they were hacked to death with a gardening hoe and another metal object.
Forensic evidence indicates that Mr Miller fiercely fought to defend Ms Witheridge, whose blood was found on the hoe that was recovered near the bodies.
Another weapon believed to have been used in the killings has not been found.
Police regional commander Panya Maman admitted police investigations have to start from scratch after DNA samples did not match any of 12 suspects.
''We still believe we will bring the attackers to justice,'' he said.
General Prayuth's comments questioning the safety of female tourists in the country following the murders triggered uproar in social media and prompted the British embassy in Bangkok to raise ''concerns'' over the remarks.
''They think our country is beautiful and safe so they can do whatever they want, they can wear bikinis and walk everywhere,'' General Prayuth said. But ''can they be safe in bikinis . . . unless they are not beautiful?''
In a rare moment of public contrition General Prayuth said he did not mean to cause distress.
"I didn't intend to insult or criticise anyone. I just warned that sometimes people have to be careful . . . today Thailand is safe except there are some bad guys - like anywhere else in the world.''
While Thailand is known as a hub of sex tourism, General Prayuth's comments reflect deep conservatism among the country's strict military rulers.
Thailand's tourist arrivals have dropped 10 percent since the May coup with martial law still in place across the country, while curfews have been lifted.
Following the murders, authorities have banned all-night rave parties on Koh Tao, which developed as a spin-off of ''full moon'' parties on neighboring Koh Phangan that attract up to 30,000 revellers.
Criminals frequently target young foreigners, including Australians, at the parties where drug taking, spiked drinks, alcohol abuse and corrupt police shakedowns are common.
Many of the crimes are not reported to police.