It was exactly a year ago that the bodies were discovered on the beach: nearly naked, their blood mixing with the morning surf.

Hannah Witheridge was a beautiful blonde from eastern England. David Miller was her handsome friend from the Channel Islands. They were in their early 20s and vacationing together on the tiny tropical island of Koh Tao, a backpacker’s paradise off the coast of Thailand.

On Sept. 14, 2014, they attended an all-night party on Koh Tao’s idyllic Sairee Beach: a half-mile swath of emerald water and white sand. Sometime deep into the night, the two friends wandered off, perhaps headed back to their bungalow resort nearby.

That’s when the killers pounced.

By the time dawn broke over Koh Tao, the beach had been transformed into a bloodbath. Witheridge was found with her face smashed in, her skirt wrenched up and her body showing signs of rape. Miller was found four meters away: face up, with a blow to the head and water in his lungs.

A rusty hoe, its blade broken and caked in gore, lay nearby.

The killings roiled Koh Tao, an eight-square-mile island buoyed by tourism. Authorities scoured its jungles for suspects as islanders blocked the ferry to prevent the killers’ escape. Coming just four months after a coup had installed a military junta in power, the case quickly became a litmus test of the new government’s commitment to fighting crime.

One year later, those test results are far from convincing.

Two Burmese workers are currently on trial for the tourists’ grisly killings, but the case is quickly unraveling in court. On Friday, a Thai forensic expert said that DNA evidence from the supposed murder weapon does not match that of the suspects.

The testimony is just the latest in a long series of shocking setbacks that threaten to sink not only the case, but also the Thai criminal justice system.

From the beginning, there were signs that the investigation was in trouble.

Thai police admitted to moving Miller’s body, ostensibly to prevent it from washing away. Authorities announced that Witheridge was raped, then said she wasn’t, before finally saying she was raped twice. Cops initially named a British friend of hers as a person of interest, then began taking DNA samples from hundreds of suspects. The investigation descended into the absurd when Thai Prime Minister Prayuth Chan-ocha commented on the killings by saying that only ugly women were safe wearing bikinis in Thailand.

Finally, police appeared to have found their footing when they arrested two Burmese migrants who, police said, had confessed to the crime.

Yet, that case also has been disintegrating from the get-go, like a courthouse made of sand.

Shortly after arresting the two 22-year-old Burmese men, Zaw Lin and Win Zaw Htun, Thai officials had the suspects perform a bizarre public reenactment of the crime. As police linked arms to keep onlookers off the beach, a confused-looking Zaw Lin and Win Zaw Htun fumbled to reenact their alleged crime. Wearing helmets, bulletproof vests and handcuffs, and wielding a dust bin instead of a hoe, the men demonstrated how they had supposedly killed the two tourists. Bystanders, including a TV reporter, were roped in to play the the victims.

But their confession was, itself, confused. The men said they didn’t use condoms, even though police insisted they had.

Then, just a few days later, a lawyer for the two men declared that the confession was false: Police had beaten it out of them.

“They told me that they were on the beach that night drinking and singing songs,” said attorney Aung Myo Thant, a Burmese Embassy official, the Guardian reported. “They said they didn’t do it, that the Thai police beat them until they confessed to something they didn’t do.

“They’re pleading with the Burmese government to look into the case and find out the truth,” he added after speaking to the two men. “They were a really pitiful sight. Their bodies had all sorts of bruises.”

Doubts about the case against the migrants — and the underlying mystery of who killed the tourists — have only deepened since the trial began in early July.

First, Thai police admitted in court that they never bothered to check CCTV footage of a boat leaving from a nearby pier just an hour after the killings.

“We have the footage, but we never checked it,” Police Col. Cherdpong Chiewpreecha said in court, drawing gasps from those in attendance, according to Sky News. He said he simply didn’t believe the killer would have taken the boat.

Cherdpong also said that his department had not investigated rumors of a fight between Witheridge and the son of a powerful Koh Tao politician the night of the killings.

Nor did his department fully test the alleged murder weapon. Instead, the colonel told the court that the hoe was examined under a magnifying glass but that investigators decided there were no viable fingerprints or DNA to collect, according to Sky News.

Blood spatters were not tested, Cherdpong said.

Finally, he said he didn’t think it was relevant that CCTV footage showed men fleeing from the area in different clothing than what the Burmese workers were wearing that night.

Last month, the interpreters who were used to obtain the now retracted confession admitted in court that they are actually roti (pancake) vendors who barely understand Thai and speak little Burmese, according to the Myanmar Times.

“The second roti seller has been on the stand today, and it’s become very clear that he does not have much of grasp of Thai at all, so we don’t understand how he could have translated for police,” Andy Hall, a British migrant-rights advocate who is assisting the defense, told the newspaper. “As well there have been many police procedural issues exposed this week, including many inconsistencies in the timing of events around the arrest of the accused.”

Then came Friday’s bombshell about the DNA on the bloody hoe.

Police had previously given conflicting statements about the DNA evidence, initially saying that it was lost or “used up” before later insisting that it had been properly saved, according to Reuters.

Last month, a court on Koh Samui — 40 miles from Koh Tao — ordered that the remaining forensic evidence in the case be sent for reexamination.

On Friday, Pornthip Rojanasunand, the head of Thailand’s forensics institute, testified that DNA found on the hoe does not match that of the two accused Burmese men, according to the Telegraph.

With no DNA evidence and a contested confession, the case appears to be collapsing.

The trial is expected to conclude later this month. Given the inconsistencies in the investigation, however, doubt is likely to remain no matter the verdict.

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